It took some effort to familiar with your england, but I do understand what you r trying to say smh.
UBS (accounting module) has a very bad rank in Msia, for experienced account clerk they r gonna have a smooth learning curve no matter which accounting software u give them, because all accounting software use the same workflow, just minor difference in GUI.
Ads and sales tell you the features and quality of a software. How to determine the quality of an accounting software?
1. Locking mechanism. It prevents user from simply delete a transactions from a database. How easy the data gets corrupt. Does the security built up to par?
2. software features. Generic cant fulfill the specific one. No business software is generally fit for all due to different operation in different places (tax code, entities name, etc), operation flow.
3. Local software has more competitive advantage over overseas brand. Came across as a SAP consultant, I'd say even for big player like SAP, they dont have good market in Msia for many reasons not only because of price.
4. Helpdesk support - whether or not the dealer has built a strong team for the whole year support, it's important to access their company structure. I have seen some dealer who don't have a team to standby for technical support.
5. many more, too long to write ... 

Hope you will dig down in a deeper level in sourcing if you really care about the business system infrastructure used by your operation.

probably I was kinda wrong, and you are kinda right, but I'd kinda like to let you understand some points that I kinda want to highlight.

1. no such thing? Just so you know, a lot of the software out there can just let customer to delete a cash bill/ invoice/ voucher etc. This is so call locking mechanism.
Whether or not the user want to reverse journal or delete invoice, that's an option by the user.
Good accounting software should never allow user to delete any transaction (invoice/ voucher/ receipt). What I kinda like to mentioned is about did the software has such restriction or not. Not about reverse journal. 
Refer to the SAP Community Network, there are many info about how a user should reverse the transactions in the event of wrong entered. One thing I like about their software is that the entire software is so strict, and it never give users a chance to delete any transaction. Sad to say that our local accounting software design is go down to the drain, the software engineer did so just because the customer said so. Somehow they were being called the R&D, in fact they have development, but not research.
2. Tax depend on country? What are you trying to say? Of course all of us knows that tax system varies in different country. What I mentioned is feature. For example, you get used to the bidet in Malaysia toilet, but when you travel to the Sg you realized that there is no bidet in their toilets, u blames that why the public toilet don't have this kind of features. This is what I wanted to say "PRODUCT FEATURE". Tax feature is actually only the tip of an iceberg.
You are like want to argue, but with no point.

3. I kinda dono what you kinda dono. What I kinda tried to say is local software is more favored by the local business due to price, software features, local support team, marketing nuance, customers who bought the software because they knew the boss, etc

4 and 5 I don't wanna repeat again

Accounting software is a tool, so important for the business. Selecting which software for your business is more than meets the eye. Ayam promote liberal, and ayam hope to listen to more point of views (solid one) instead of emotional judgment.

No transaction should be deleted even it has never posted.
1. This is going to create inconsistency in the database. Think about the document number, imagine you have more than one user who doing the data entry in more than one place. It's no feasible to design a system to find out what is the next document number should be adjusted back on track. I've tried multiple brand of accounting software, and all I seen is that user need to manually set the next document number. Imagine the user do it quite often, he's going to spend time to check with the rest of the users in other places.

2. For audit trail purpose. Same document number appears once, I don't think it looks nice to the auditor. Not even Kastam. Came across big international software. They never allowed to delete any invoice from the system. But they do have work around such as CN, reverse journal

I didn't mentioned about technical, if u have that problem, you should work it out hands in hands with your vendor perhaps. Or your boss cut your salary to pay for a more sophisticated network infrastructure, or you stop blaming the software vendor while sit there for doing nothing. That is something related to the LAN-WAN performance, most of the time not caused by the software.

One thing I heard is not many clerk get used to UBS, because of many special transactions need to manual pass JE. Manual pass JE is easy for account clerk, but not for normal clerk who is new to accounting.
I'm not sure how bad is UBS, I've seen they printed ads on the bus, aired on the radio. Good software should be focused on its engineering business instead of throwing money for marketing campaign.

It sounds like you have agreed to the point that deletion of invoice shouldn't be allowed. 
Server hang issue most likely not due to the software, I have never heard of the theory junk of pile code. And I do believe any mainstream computer can do the job, unless you are using pentium 4 that kind old spec. The performance mostly depends on the connection between server and client. Modern computer users are multitasking, internet radio, cloud drive, email, these are the apps that sucks up the bandwidth.

I've never heard of pile junk of code, maybe you are trying to say the slow performance due to too much processing job in the server.
Some application was designed to put more processing in the server, and vice versa. When the server takes all processing jobs, that is consider thin client. On the other hand, if the processing jobs shared by the client app in the end user's PC, that is consider a fat client, the server wont be too heavy of workload, it reduces bandwidth consumption.

I recently heard of a quite successful accounting software Wavelet EMP, it's using AWS (Amazon Web Services) platform cloud based to run the accounting software. User is able to open up the apps anywhere to connect to the server. Good is the scalability, the power of the server can be upgraded or downgraded anytime with just a request to the data center.  No more hassle to add RAM, add hard disk.

I guess there will be more accounting software go cloud-based.

With decent computer spec, the size difference of a installation file doesn't really make a difference, imagine u have a hard disk space of 250 GB, even that installer is 500 mb, it still doesn't make so much difference, what matter most is the architecture design of a software.
Fat or thin client is a concept used by big ERP like SAP/ Oracle/ Microsoft. That is an option where the user environment has connection constraints, and the client PC takes up some of the processing works to reduce burden in server.
Btw, Wavelet EMP stands for Enterprise Management Portal, that is an ERP system also. Local software house, and they doing quite well in China.
Terminology is very important in software development, someone experienced coding like u also know that right. Terms must be very clear in every page of the system. ERP and MRP are general terms used to described these software, there are many brands out there able to perform the same jobs.

Chart of account shouldn't be hard coded in the system, that is a big no is for an accounting system, different accountant want to have different set of CoA, what is good for one company might not be good for another.

Terminology is the basic knowledge you need to learn before starts development.
Current cheque is current cheque, PD cheque is PD cheque. Even the business operation workflow often change, but terms in accounting are not changing drastically.
If u know how to build a software, but u didn't differentiate the terms, u r gonna build crap. If u r not good in coding, but u understand the business process terms n workflow very well, u still can work out with someone else to build a good software.
Life is really simple, don't insist on making it complicated. 

The real world is there are many decent accounting softwares that are flexible in setting up CoA. For example QNE Optimum:
https://youtu.be/WLcHmImi5oo
And all the big software out there are doing so. Just so you know 

Of course PD = Post Dated cheque. Would you consider PD cheque as Port Dickson cheque in you software? 
Nowadays people are so Confucious wannabe, in a way when they are not able to convince, they try to confuse.
Life is really simple, don't insist on making it complicated, brother!

Hi, anyone heard of Sun accounting system? Does it msia gst compliant?