>>58338486Beta builds suggest it was more to do with lots of late changes. After GS rebooted development, a lot of mons were cut. Some were only added in at the very end of development.
The Masuda period of GS development was focused on map design, story beats, and improving presentation. Because of the constant cuts and changes to the Pokedex, game balance was never perfected. It's why lots of trainers use Kanto mons.
Unlike Gen 1, those late Gen 2 mons had to work for the anime, merch, and games. But because they were late, they were unbalanced or treated more like easter eggs