4-3-3 would only work with the correct players in the middle of the park. If you take Pogba out of it, there's no balance to it at all, too many players doing pretty much the same thing. No runners from midfield (I don't count route 1 to Fellaini). Pereira would be a good back up/rotational option to Pogba, could easily play in the middle as a creative ball carrier. Veratti, Bakayoko & Pogba would be in a midfield 3 would be monstrous, compare it to Herrera, Fellaini & Pogba...
But those two signings, along with Greizmann, is just too unrealistic for me. That's why I think 4-2-3-1 is the logical choice, as we already have most of the puzzle for it with the likes of Mkhi, Mata, Martial, Rashford, and potentially Griezmann to have in that line of 3 behind Zlatan/Str. Just buy one world class midfielder to partner Pogba, get Griezmann (hopefully), and a centre half if we're offloading.