I mean, both your examples have alternate justifications. Hoenn starter trio got completed in ORAS because it was a Hoenn remake. And then the G-Max Kanto trio was only completed after a huge outcry as to "if Dexit is gonna be a thing, don't make it so blatant that Charizard is your favorite" after the base game released (whether or not Game Freak heard that outcry, I dunno, but the fact that G-Max Cannonade and G-Max Vine Lash basically do the same thing as Charizard's G-Max move, shows that maybe they didn't originally plan those forms.)
Also, both those examples are from before PLA's release, when starter trios were more concrete.