If the Pokemon universe had an all out war between regions, which region(s) do you think will survive and which would fall? I’m not really talking about nuclear bombs and guns and stuff like that but the species of Pokemon in that region and how well they do against other Pokemon from other regions, the competency of the gym leaders, elite four, and champion, etc.
The thing about Pokémon trainers is they make terrible soldiers. They all have wildly different capabilities, so it’s difficult to assign them tactical and operational roles. They’re competitive and a lot of them have huge egos, so they tend to have poor discipline and unit cohesion. Their individual battle styles and the different powers of their Pokémon will often work at cross-purposes if they haven’t been training together extensively. Their deep emotional bonds to their Pokémon can be a blessing and a curse; they’ll fight harder to protect their friends, but they can’t handle casualties. Old-fashioned honour duels between small numbers of elite warriors like the warlords of feudal Ransei are one thing, but in a modern conflict between large, well-equipped armies, you want a substantial number of soldiers with similar or identical capabilities, drilled to work in unison. Run-of-the-mill Pokémon trainers can be good at asymmetric warfare, and the best ones can be useful for special operations, but in a pitched battle they’re a nightmare for commanders. Don’t think in terms of some douchebag with a Dragonite flying over a battlefield dispensing Fire Blasts or whatever; he’s a huge, obvious target and is probably causing a significant number of friendly fire casualties. Think in terms of a squad of trainers, all with the same mid-level Pokémon and all using the same techniques. That’s why Lt. Surge famously evolved his Raichu so early, before it learned any speed techniques – they were supposed to be optimising themselves as cogs in a machine, not as individuals with unique talents. If you have a bunch of Pikachu and a bunch of Thunder Stones, those Pikachu can all get stronger in a predictable way, instead of introducing all kinds of vagueness as a result of their individual training and experience. If you have the stones, it’s very quick and easy.
That doesn’t answer your question at all.
I’m not sure I have a good way to answer your question.
Look for Pokémon that can reach their potential at an accelerated rate, look for Pokémon that fight well in teams, look for Pokémon that can alter an entire battlefield in a way that will support their allies, and look for Pokémon with a predictable and obedient temperament. Where you find a lot of those and can put together a sound strategy that lets them work together in very large numbers, that’s where you can build a powerful army.