I just wanna go ahead and mention that Timber's been away for a while, so of course things changed, updates, the AI sucking, and other stuff. But only she shall update that herself, and consider that she isn't here, it shall stay they way it is for now.
As for what I've read so far, I shall only say this:
The level cap helps preventing this:
more than anything. What difference would make Julia's pokemons having competitive move-set and good items, if you can just get a starter to it's last evolution before the first gym.
Regardless, you're still right. It's also to make sure you swap your pokémons around, and have a strategy that doesn't rely on overlevelling your pokes and power through the gym leaders/important battles.
I must also admit that I still have to use a Common Candy on my game. They're probably all rotten in my bag or something.
I'll stick around for this too~