That's the issue. We want to add a proper winger. People wanted talent players who would prefer drifting inside. As far as proper winger being concerned (both offensively: stretch play, provide crossing, combine with full back; can play on both wing; & defensively: cover well for the full back), Perisic appears to be one of the best in this rare breed, where wing forward is the fashion & younger generations try to emulate Ronaldo/ Messi & can't play winger properly.
Regarding the formation, people show more love for player & become irrational. Even in 4-2-3-1, Herrera can play with Pogba & another defensive central midfielder in a rational way. Remember the Everton game at home? The game ended up with Herrera playing some weird narrowed RB, when in defensive phase he was still a midfielder. He even stepped up & delivered some serious crosses just fine
---------------------CF-----------------
Perisic------------------Micki
------------Pogba------CM--------Herrera
--LB--------Lindelof----Bailly-------------Valencia
Some kind of diamond with Perisic & Valencia to provide width. LB should play narrow. If Perisic switch wing, then the opposite with Pogba play wider... The CM position is interesting. Now seeing the formation this way, someone like Dier does enable maximum flexibility in the tactics. Fabinho isn't too bad neither with him can play as RB. With Fabinho, I think there is still room to add another CM. I prefer that to be left our youngster like Pereira, Tuanzebe (even as makeshift)