While I agree with you that his move and defense weren’t gigantic factors, a good move even not picking a guy off can slow advancement on hits.
i think His success was mostly due to his command, and his controlling the tempo of the game. When his command was off a bit, he usually got tattooed.
as for FIP and xFIP, I wouldn’t be too concerned about it yet. Lopez ever gets a little command, his k rate will skyrocket, and his walk rate will drop. I think the concern with Fulmer and Giolito is it seems more often than not, they cannot come close to hitting their spots, and now it looks like the are going to start running like crazy on Gio.