I think its pretty comparable. Especially since the current itteration of GS seems to be made for mobile devices.
Cutscenes seem a bit slower loading when I compare them to FKG, but honestly that might be not related to performance, rather there might be intentional pause built into the dialog windows.
Try it out and you`ll see how it performs on your machine. And if you participated in the year long pre-reg gacha and got yourself some free rainbows, then thats yet another reason to give it a go and see.