I’ll be very happy with either.
James Wyatt led Theros, Fizban’s, and Bigby’s, all among my favorite 5e books. I use them all the time and they present wonderful DM toolboxes.
Jason Trondo led the Book of Many Things , and it was absolutely fantastic and an inspiring read.
If I could pick only 2 WotC designers, I’d pick these two. If they are sharing credit on this, I think it’s in very good hands.
If we are hypothesizing on calendar, Wyatt shared a co-lead spot with Amanda Harmon on Dragon Delves, right after sharing co-lead with Chris Perkins in the DMG, so I’m not sure there was time for him to lead FR. If James did do it, that might explain why Dragon Delves is so much blander and less inspiring than his usual work, as he would have been split across multiple projects.