It's a little bit more complex than that but you got the idea.

My tenant raked up the electricity bill to RM30k and then left and although the tenancy agreement showed that I was not the one using, TNB said I may be able to convince TNB of not suing me to recover that RM30k but as for any electricity to be supplied to the property, the RM30k has to be first settled, TNB don't care by who.

So, there are 2 parts to it:-

1) having the tenant registered an account for the supply effectively ONLY absolve you from any legal liabilities in terms of recovery of debt but this would put you in a position of having no control whatsoever over the account (eg: no knowledge about any outstanding owing, if any); and

2) whether the account is registered under the owner's name or the tenant's name, there will be no further supply to the property if the supply was previously terminated/suspended because of unpaid outstanding unless they are first cleared in full/partially.

... therefore my new tenant will not be able to register an account for the supply of electricity to the property.

In this arrangement, TNB will not be bothered in attempting to find the tenant and sue them (which by right they should, legally speaking) because they know eventually the owners will pay up because no owners will leave their property untenanted for years which is the reason why I lamented earlier that this "rule" that TNB relies on is abusive in nature (literally holding owners/landlords by the balls) - it is also potentially highly exploitable as well in the sense that TNB could easily let the tenant continue raking up the charges, pretend to be ignorant and then put the owners/landlords in a position where it leaves them with no choice.

To your question; do you know that you have no power/control whatsoever over an account that is not registered under your name?

Imagine this, you see from your mobile app that your tenant is piling up the electricity charges every month and your demands are not being heeded. Naturally, you would want to do something (like asking TNB to terminate/suspend supply) but sadly you cannot because you are not the owner of the account and TNB probably won't entertain you.

So, in this circumstance - you will be at the mercy of your tenant.

paid the outstanding left behind by the errant tenant from my own pocket - not worth arguing with TNB when i'm losing the opportunity to rent my property out.

moral of the story is, take care of your own property whether the account for the supplies of utilities are registered under your name or not because at the end of the day, tenants gets off scot free (especially more so with the Temporary Measures For Reducing The Impact of Coronavirus Disease 2019 (COVID-19) 2020 Act.

There is no standard treatment. In some cases TNB connect back the supply when there is tenant's debts, in other cases they force the owner to pay. Maybe the criteria they use is how much the amount owing if there is any criteria at all. Or it could be just different TNB offices having different practices.
Yes, it's true that the arrears will be the tenant's responsibility meaning that TNB cannot legally chase the owner for payment. But they have other ways to twist the owner's arm to pay.