Speaking of the Elite Four, I really hope for some improvement in that area. To be honest, Gen. III had probably the worst-designed Pokémon League challenge of them all (maybe second to Gen. II, though).
Once you arrive there, anything with a weakness to Water (or a not-very-effictive-ness against Water) is severely underlevelled. Upon passing through Victory Road, you can challenge the Elite Four, and find out that they probably outlevel you by some margin, or that they're a little too tough to take on right then.
"That's okay! I'll go train somewhere!" you think. That's when you realise that not only do the Elite Four outlevel you, they badly outlevel everything else in Hoenn too. Where do you go to train for the Elite Four challenge? Any Trainer's Eyes rematches have their Pokémon at level 40, tops (besides, those rematches are annoying to initiate). Gabby and Ty have their two Pokémon at level 39. In the very depths of Victory Road you might find some wild 'mons at level 44, but they have a low Exp. yield.
Basically, you're stuck grinding against weakling 'mons and -trainers unless you feel like throwing yourself against the Elite Four time and time again to slowly level up. Hoenn's Elite Four are made challenging only by the fact that they're infuriatingly tedious to prepare for, and that's terrible game design.
At least it's nothing against the chore of levelling anything beyond level 80, though. Once you beat the Elite Four in R/S, you find out that nowhere in the game are there any better places to train, and the Elite Four levels remain capped out at 58 or below (way below, in Sidney's case).
I like to scold D/P for their numerous shortcomings, but at least they had the Vs. Seeker.