Well, I'd like to offer some thoughts about all you said. I tend to think otherwise about this subject.
Firstly, AI patterns tend to be tricky. Without going through the code and these infamous function crawls, it will be hard to know for sure what the AI is aiming to at these specific moments. Personally, I've always considered that AI was predicting a switch. So, if you're playing on Set Mode and want to keep your mon alive, these AI's choices could be efficient. In general, if you find something odd in AI's choices such as picking wrong moves, you should make a specific thread about it. I'm sure there are a lot 'wrong choices' left.
Secondly, about items, I just find them cheap. Everytime I had to stall with potions or revives, I considered the battles lost. This was not the case during my first playthrough tho Anyway! This is why I won't complain if AI don't use items since I don't use them myself anymore. Maybe it's my casual competitive spirit.
Lastly, the several Gen 7 changes may have led to easier battles ... But I don't think it's actually the case! It's hard to state that for sure without collecting data on several players. Plus, it mostly depends on the matchup. I don't think a lot of people used the exact same team. I just feel it a non-issue. This is why I feel that "getting used to the game" is a better answer. But I would even say that people simply got better at pokemon. After a Reborn playthrough, you should have a better time getting through other difficult fangames.