Does it feel like, to anyone else, that Gen III Pokémon don't get very much love compared to other early generations? Like yeah there's a new form here and there, but most of it is just Mega Evolutions, which are temporary forms that not every game is going to take advantage of.
Discounting Megas like that is a pretty big asterisk. Gen III Pokemon literally have the most amount of Mega Evolutions because of ORAS.
Gen III - 20
Gen I - 15 (13 if you count Charizard and Mewtwo once)
Gen II - 6
Gen IV - 5
Gen V - 1
Gen VI - 1
Even in just XY, Gens I & III were tied for the most if you counted Charizard and Mewtwo once. And also there was Groudon and Kyogre getting their Primal forms which are basically under Mega under a different name. And the only wave of new forms introduced since then were Gigantamax forms, and only Gen I & VIII Pokemon, Melmetal, and randomly Garbodor got those. If anything, Gens II, IV, and V are the ones getting the most screwed here.
And then I guess we can talk about regional forms too. Counting it by just final forms:
Gen I - 22 (24 if we count all the Tauros forms separately)
Gen V - 7
Gen II - 5
Gen VI - 2
Gen III - 1
Gen VII - 1
Gen I has gotten the most by a large margin, and Gen V has quite a few, which I guess serves as consolation for getting ignored for Megas. But Gen III isn't doing any worse here than other Gens. In fact, Gen IV is getting screwed the hardest, no regional forms at all unless we count Sneasler as like a counterpart to Weavile.
Cross-gen evolutions? Let's count them up in a really simple way (if they got multiple like Eevee or Porygon we'll count them once, and we won't count new baby forms because you don't really use those).
Gen I - 19
Gen II - 12
Gen III - 5
Gen VIII - 2
Gen V - 1
So yeah, Gen III hasn't gotten much there since Gen IV, but also later Gens aren't any better, most cross-gen evos have gone to Gen I & II Pokemon by large margins. And again, Gen IV is getting screwed here with none at all, while even Gen V got one with Kingambit in Gen VIII.