I'm moving my game from a turn based RPG (close to Pokemon in idea) to an action RPG (more zelda oriented) and honestly, I love the change already.
Not just does stuff look and feel nice, I also save so much fragile code and timing, to make the turn based stuff working (saved about 80 lines of code or so and now it's maybe 20 total for all movement stuff)
And I mean, you can do 3D games in GMS2, sure. Nobody will prevent you from that.
But honestly, other engines (like unity) are made for such purposes and provide more guidance and tolls.
Other way around, if you want tile based 2D action games, unity is really not your friend.
Sure there are addons to allow it, but GMS2 has more tolls right from the start and is literally built with that in mind.