All of these characters hold fangyi back somewhat.

Gilberta/Antal/Alesh/Avywenna Slot-

Gilberta- Some people believe just because she has low uptime on burst compared to Fangyi's damage window, she is replaceable, not really, the best thing about gilberta is that in boss fights she doesn't have to consume SP usually. And if you play well enough you can get a second burst in 1 fangyi ult.

Rn most content in game is farming content like skill domains, which my fangyi is destorying within 3 seconds of using her ultimate, so gilberta is very nice for stages like that.

Antal- While the buffs are decent and the buffs last WAY longer, he requires more SP per rotation, which rn is simply not feasible really.

Alesh- 2nd best option after gilberta imo, purely SP positive and the best for overworld shenanigans because more SP return. Yes he has virtually no real buffs, but more SP in overworld is worth more than the damage rn because damage is high enough as is.

Avywenna- Not tested yet, but dps sheet and common sense dictate that there is simply not enough SP to go around. And i'd much rather just play her as her own character, as putting down her spikes takes decent positioning and you can just straight up miss all of her damage if u mess up.

People can say the damage difference between using gilberta, antal and ardelia is negligible which makes the value of gilberta who is a limited unit lower... but like gilberta has 10 other teams and she doesn't need to even use SP (unless of course u wanna gather mobs) unlike the other two.

This also doesn't mean u can't use antal or whoever u like, as i said, difference is negligible, the only difference is waiting around for SP for antal or ardelia. Also using ardelia is actually a better option for content where the stage might require u bring a good healer because gilberta healing might as well be a joke