One of the main problems we seem to have with the 4-3-3 is where to fit Messi. The main problem with 4-4-2 is the lack of width and not being able to fit in Dembele and Malcolm. I know it's unlikely to happen (though Enrique did try it a couple of times), but I wonder if we would be more suited to a 3-5-2 with the personnel we currently have. The reason I was thinking about this was that with the way our wing backs play, we sort of play with wing backs rather than LB/RB anyway - However, what happens to us in counters is that there's often an overload of players on one side, and a sort of meaningless overload which doesn't really help us (a cluster of players not contributing to the play and yet out of position defensively) - this leads to opposition running at our 2 CB's.
With a 3 CB system, I think there could be more balance in attack and defense, keeping in mind the players we have in our roster.
Something like-
--------------Lenglet--Umtiti--Pique
Semedo Rakitic/Vidal Bob/Busquets Alba
----------Messi/Coutinho
Dembele/Malcolm---- Suarez
This wouldn't necessarily have to be our go to formation, but would be interesting to see something like this. You could fit various personnel like Arthur, Alena, etc. in a lot of these positions and in an offensive transition, you'd have a lot of these players ending up where they end up anyway (Coutinho on the left hand side of the D, etc.)