“Required” is unspecific as a term here. It depends on goals. (And you could say that about any exercise that isn’t a compound movement if I’m accurately following your logic. Which wouldn’t be entirely fair.)

I'll be the odd one out here and agree. They're super good but the muscle only knows tension. And that can be provided with pressing alone. Flies are great but definitely not required

Nothing is “required” for any form of development to any muscle group. So I wouldn’t even call this unpopular, just simply an opinion.