Its about how good the engine is, and how smart they devs are at optimisation.
Look at Fortnite on the iPhoneX, thats crazy how good it looks for a mobile game.
This isnt a "switch is more powerfull than people think" moment, its a ARK devs use a bad engine/cant optimis their games thingy.
Fortnite and Ark use the exact same engine. This is purely a developer thing though I hear they have gotten better at optimizing as time has gone on.