Why would you go after a wing when you have Crowder, Brown, Smart, Bradley.
It makes absolutely no sense, especially when the team still has a glaring weakness of the big man next Horford.
Because
(a) You can really never have enough capable wings in today's league
(b) It's unclear yet if Brown can really play, or if Smart will ever be a reliable offensive player
(c) Bradley is probably going to be a cap casualty when his deal is up.
(d) Nobody you mentioned other than Brown is over 6'5'' or so, and as far as he goes, see (b)
I don't agree with you that the big spot next to Horford is a "glaring weakness." Horford is the two way, multi-skilled big man the Celts needed. They need to add another productive, proven starting caliber player next to him in the frontcourt, but that doesn't necessarily have to be a traditional big man.
In fact, given that the team continues to notably lack shooting, shot creation, free throw generation, and wings with size, putting a player that checks some or all of those boxes at the 4 next to Horford would make a lot of sense.
As for how the names I mentioned compare to Love ... I'd take Hayward every day of the week over Love.
Even if you think Love is the better player -- once he was, probably, but I doubt he is anymore -- the league just isn't very accommodating for players of Love's sort anymore. Whereas every team in the league needs a Hayward type player.