Yuzu always seemed to have issues with his flip edge, so trying a quad version of it might just magnify the problem. I don’t think the quads have a difficulty based on the jump type tbh. Many people learned the Quad sal before the toe. Same for other like Nathan and Boyang who learned the lutz before the loop, and Shoma who can do the flip, loop and toe but not the sal. I’m sure he can do a flip, but it’s his least favorite jump so why would he?