>>35765751>>35766174They never really address how firearms evolved in the Pokemon world outside the anime, but at least one Pokedex entry mentions that Chesnaught is strong enough to flip lighter tanks and a tanks appear infrequently in the show.
I always imagined that soldiers in the Pokemon world are issued pre-"trained" (EV trained, flawless IVs, natures that compliment their movesets) and bred Pokemon by their governments as sort of an anti-thesis to the Ace Trainer archetype. Where Ace Trainers are dangerously competent trainers with average Pokemon, Soldiers are sort of like that guy using a competitive-grade Machamp that was discarded for Conkldurr they got off the GTS as an HM Slave without even knowing it. Pokemon with moves that would make them useful on the field but from a strictly battle standpoint are woefully underutilized and led by a standard AI as a balance.