LogFAQs > #970712776

The thing with a lot of recent 4-stars is that many of them tend to be supports for specific 5* units. Sara for Raiden, Faruzan for Wanderer (and Xiao), Gorou for Itto. In addition they tend to require high constellations for power level, quality of life, or both, and aren't as useable straight out the gate like the more generalist launch characters are.

Looking at your characters, Layla is a pretty good Cryo shielder, I don't think she has heals but she's allegedly on par with Diona who you don't have. Ganyu might like her. Heizou can also be built as a decent Anemo main DPS that works with Faruzan. Thoma is used in Burgeon teams (dendro + hydro to bloom + pyro to burgeon). And if you really want to use Yanfei because you like her more than Xiangling, you have the team for her (Yanfei/Xingqiu/Bennett and a flex like Fischl/Sucrose/Beidou) but it's not as universally strong as the Xiangling + Bennett team.

So yeah they're not bad but you can see how they're significantly less flexible, and people value that when they're limited by resin.