>>23508244
Zaku is no longer anywhere near top of the line but it still has the ability to take out a GM in normal battle, it's just much less likely to do it since it's less mobile than the GM and its beam weapons were better anti-MS weapon. But war isn't fought only as a series of one-on-one duels, so ambush tactics, teamwork, or just plain luck could maybe allow a squad of Zakus to take out a squad of GMs, but way more often the reverse would happen.

Panzer III got phased out and replaced by upgunned Panzer IV, Panther, Tiger, same as Zakus were phased out for Doms and Gelgoogs. Panzer III still saw use as variants made for specific roles though, the StuG were fairly successful, and Zakus more or less were treated as the same where they still saw usage as marine and sniper types where they're less likely to meet enemies in direct combat or at least end up fighting similarly performing opponents.

>Old grunts in late UC are nothing but fan service, while I like the idea of giving them refits and bringing them back they should have been good enough probably up until the Unicorn/Mafty era.
That is pretty much exactly how long they're still used for. Outside of that one manga page showing a Dom still operating on Earth so long after the OYW, it's not really a thing since Unicorn was supposed to be the final gathering and subsequent death of most of the earthside Zeon remnants who had lasted that long.