>>56213172Garchomp is already extremely strong, to the point where it seemed immune to powercreep for multiple generations and even now is a good pokemon even if it's no longer quite top-tier. It's also very iconic and already got a mega form so it already has an alt form that doesn't replace the original due to being a temporary transformation from it.
GF mostly gives regional forms to pokemon who need a buff and aren't particularly iconic (they gave Raichu an Alolan form but not Pikachu, because the original Pikachu is so recognizable they'd rather keep using it in the marketing instead of a new Alolan Pikachu), while already iconic pokemon like Charizard, Garchomp and Pikachu will get temporary forms like megas or gigantamax that power up the original without replacing it (if you want to use mega Charizard or gigantamax Charizard you still need to include original Charizard in your team because you can only transform it during battle, while regional forms like H-Goodra effectively replace the original).