Blowing up a tank in a single shot is a mechanic that doesn't make any sense to me.
Remember when you were the first to die at the start of a match because of a casual ammo rack? Yes.
Remember when your attempt at clutching failed because of an ammorack? Indeed.
Remember when the entire course of a match or a tournament is decided with an ammorack? Absolutely.
Giving someone a free kill out of total luck and complete unwillingness to damage a specific yet crucial module is utter BS. Who aims at ammo racks? None. This is the reason why internal module damaging is quite controversial by itself, let alone a module that blows you up, no matter your HPs, when critically hit. Imagine playing a shooter with a chance of your body blowing up with a hit to the leg.
Ammo rack blow-ups should be kept in game just for spectacular reasons and only for hits that would have killed the target regardless. There is already enough RNG in this game to decide the outcomes of many battles.
Just my 2 cents about it.
Source: https://www.reddit.com/r/WorldofTanks/comments/entpgp/some_serious_thoughts_on_ammo_racks/