So I was watching a Metronome Challenge video, and while fighting Kabu, Metronome became Circle Throw on his lead, Ninetales. Circle Throw damages the opponent and drags another Pokémon out.
Anyway, it dragged Centiskorch out, and Kabu immediately Gigantamaxed it, despite both of his other Pokémon being alive and healthy.
So do gym leaders in Galar Gigantamax/Dynamax their chosen Pokémon just whenever it comes out, and other factors such as the number of Pokémon still alive don't matter?
Also here's the video if you were curious: https://m.youtube.com/watch?v=aBxetfXX8sM