The team with Fati, Griezmann, Depay, Demir is very well built for sustained effort and work rate. Playing a 4-3-3 with 3 workers upfront might make it a pain in the ass for the other teams' backline.
-> I think the team will look pretty good upfront when the most advanced 3 will be Depay-Fati-Dembele
These are the most quality, and dangerous attackers we have got. With this trident we can terrorize most LaLiga teams.
There no other quality attackers in the squad, either as wide-forward/wingers or strikers.
Braithwate, Kun, and Collado can only be subs
-> Then, about Griezman, even without Messi, I doubt he can be of any use on either wing or at CF in a 4-3-3.
He has to play centrally AND not be the most advanced attacker, but rather have Fati or Braith or any striker in-front of him.
He is an AM, not a winger/wide-forward or striker.
Hence, he will never fit into a 4-3-3.
Only chance he works out is if we play 4-2-3-1 or variations of the 3-4-3 with him in the hole.
-> Exactly the same goes for Coutinho.
-> Finally Pedri and Demir are wonderful players, but both are 8s, or CAMs, and not wingers.
Even when Demir plays on the wing, he plays the position not as a winger, but as a midfielder.
Pedri did the same last season whenever Koeman used him on the left wing at the beggining.
Conclusion: Only Ansu, Depay, and Dembele can function properly in the 3 most advanced positions of a 4-3-3