>DS sells almost twice as many units as the GBA
>DPPT outsells RSE by a decent margin
My hypothesis here is that the reason hoenn fans shit on gen 4 is because they're jealous of what DPPT/HGSS had. Gen 3 came around at the end of pokemania and pokemon was doing way worse than before, especially with the difficulty of transferring other pokemon. Because of this, pokemon started becoming more niche and instead of having a friend group who played pokemon, you'd be lucky to have one or two friends who was into it. Gen 4, on the other hand, was on the DS, which is currently the second-best selling system of all time. Everyone had one of these back in the day, even relatives who were "too old for video games" because brain age existed. Because of this, it was LEAGUES more acceptable to play video games in public and, thus, groups around the game formed more easily, especially since connecting was so much easier to do.
Maybe the reason hoennfans hate gen 4 so much is because they missed out on the camaraderie that came from gen 4.