1/4 the Pokemon in Ruby/Sapphire were returning pokemon like Vulpix, Machop, Tentacool, Geodude, etc.
While I agree that Ruby/Sapphire (and more importantly Emerald) was the biggest change the series has seen, I think you're kind of basing a lot of those views on popular internet 'generalizations' of the games.
And personally, I hardly thinkg triple battles and allowing people more freedom in WiFi battling is making the battle engine 'way more complex'. If anything, that sounds like the weakest jump the series has made yet. Why not just make 4x4 battles? Or 8x8 Battle Royale grunge matches with all Pokemon at lvl 100 cap.
Until the series starts actually altering the actual battle 'engine', all the changes they make are small because they only alter things outside the battle engine. How your pokemon interact with other Pokemon, how you level, how you fight NPCs, altering the number of pokemon/items/moves you can use in battle. These are limitations, not 'improvements' to the battle engine.
Six upcoming games you should look into:
