This is an interesting question and I share your sentiments exactly. Lets discount external forces be it political will, foreign intervention and just discuss purely on if they actually go to war.
First off what is sg objective in attacking? What are the main and secondary strategic objective? This will determine the length of the war. What will be Msia objective if they attack SG? This will determine how forces are deployed. Sg possess lst/lpd are more suited for invasion as compare to Malaysia. Msia strategy in my opinion is not to go 1 on 1 with Sg units initially. More like a delaying tactic to regroup. For every asset Msia has Sg has a counter if you look carefully. Msia armor would most prob be used for troops support rather than traditional MBT as they would be easy picking to Apaches under AA umbrella. If it degenerates to jungle warfare, they have even limited use. Sg would most prob hope a decisive battle to neutralise Msia main assets with focus on achieving air superiority. I think they have some forces based in Thailand too and that would lockdown some of the northern assets too.

In any case the battle would be fought by both with the element of surprise much similar to Japan in WW2. Sg need to push into Msia and fight there and project force to tie down Msia assets. Couple with rapid deployment of AA umbrella, Sg in Johor would be quite secure. Msia tactics could allow this to happen so they can envelop SG bypassing Johor and invade from there. I believe total surprise can be achieved. Look at how they fumbled with MAS 370 which went undetected and no jets were scrambled to intercept. That tells a lot about readiness. Yes we might have the best equipment but if not utilised properly has no strategic value. Msia will be overwhelmed initially and response delayed. The current command structure need to go thru many levels before a proper response could be delivered. Local commanders imo is hand tied until authorisation is given.

In my opinion, SG will win in the short term with better assets and training and need to quickly achieve whatever their objective before Msia can regroup and win the war of attrition. Much like Japan in WW2 they cannot afford to replace lost assets and Malaysia once they regroup and reorganise will grind out a win in the long run.

I hesitate to comment on Msia as the capability is a suspect unlike in the old days some units can go toe to toe with the best units in the world. I have no problem with the capability just the crop of current leaders do not show the required wisdom to use them effectively. Msia in a way is handicapped if it wants to take Sg. How to take a city state without destroying it? What strategic value if you raze it to the ground by urban warfare? Malaysia's main advantage is time. Delaying SG from achieving their strategic objective b4 external forces start to force their hand. Pushing into Johor would be a huge burden on logistics and guerilla warfare can seriously disrupt the sustainability. Imo if SG dont achieve their objective within 2wks they already lost. Msia is disorganised most of the time, something like this would galvanise the people into a single purpose of defending the homeland, mat rempits included . So psychologically, Sg cannot win the hearts and mind of the people rather it is like awakening a sleeping giant much like US in WW2. Common people who are united by a single purpose and this gives rise to guerilla warfare and coupled with JMF would buy valuable delaying time to organise a response. The philosophy is not to win every fight but make it less incentive for your enemy to continue

You are right in a way but have not explained why would MY capture SG. What strategic objective to be achieved? Capture in a day? Have you seen urban warfare? How it bogs down troop movement? Give you an example, Battle of Ramadi, how long did it take to clear sector by sector. Too many simplistic assumption. Mass troop movement will not be detected? Maybe spec ops in SG to remove certain incriminating evidence related to IMDB more likely.

I know it is pointless article but it sure is interesting to hear what others have in mind on IF it happens. It is what armchair generals relish.

So what if the Mersing Line is a red herring? Attack the enemy where he isn't. Supposed 3rd CAD gets hit first and is the real target? So MY is going to mobalise 3rd Div in a decisive battle? You just reinforced my opinion on defensive delaying tactic that CAD is positioned in such a way that it is far enough to overextend the enemy reach while still close enough to engage. Are you assuming the 3rd division placed so far to SG can hold southern Johor preventing it from being overrun without overextending itself? Not familiar with MY SIOP so do not know how fast they can react until proper authorisation is given. Cant just mobalise at will. It would take more than a division to hold while others regroup.

Imo a good commander would not do spec ops in SG as it entails v high casualty. Then again we got a lot of macho wannabes would do anything to succeed. So if we can work out the casus belli for this battle then it would give a clearer picture on force composition, utility and tactics.

As stated, I am commenting purely from a war POV while leaving out social, economical and political influences. If it really comes to fruition, not just sg would suffer. Thats why I mentioned strategic value for the reason for war. My simple assumption is we have what they need. They dont have what we need.