Not just Greaseman but Umtiti and Dembele too
I wouldn't sell him
sure, he doesn't fit in the current Barca front 3 (not actually sure who would, we'll get to that) BUT hes one of the few players who actually 1. works his ass off and gives 100%, 2. hes not an amigo and 3. hes a world class player without a CL to his name; he'll be motivated.
if we pair him with 2 forwards who actually run, stick to their positions, help defend and move off the ball, we'd see a totally different player. Suarez-Messi is the problem. you can add any other forward to our frontline - Neymar, Mbappe, Sancho, Martinez.. it will be the same story...
Something like this
I think if we're going to buy Lautaro (I'm pretty sure we will at some point) and if we don't sell Griezmann, I agree with you that the 4-3-1-2 is the best setup until Messi retires.
Lautaro has the experience and played well in that formation with the Arg National team with Messi and I'm sure Griezmann will be more suited for that system.
The fullback really have to be more attack oriented than usual to provide width while the 2 interiors need to have the skills to cover the space that the fullbacks have left.