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Concerning the matter of pokemon AI, the system the games already have in play has several preset "levels" of AI for in-game trainers to use. Usually enemies have a really stupid AI, while the more difficult ones are saved for ace trainers and bosses and the likes. Wild pokemon use moves at random.
Having a mode where more enemies employ the higher levels of AI would not require mountains of code, I'd imagine. I've used third party programs to change the difficulty level of enemy AI in rom hacks before, it's not a complicated system. In addition to this, do as in the challenge mode of BW2: systematically raise pokemon levels, give gym leaders more capable movesets. Of course that would require work to be done, but it's exactly what's being asked for. And they've practically been doing this in XY already, except in reverse. Giving trainers such as the rival characters intentionally bad movesets (look up Tierno's team, I dare you).
See, this is the root of the problem. In XY, the developers have actively tried to make the games easier, for the sake of accessibility. This has been explicitly said several times in interviews. And it's honestly making me quite concerned.