We've already got rid of 3 wide men in Izquierdo, Ali J and Tau so there's definitely a place for March in the squad, even with Cucurella.
I think Solly has worked hard at his game, but I've always felt a little uneasy with his defending in and around the penalty area. It is clear he is not a natural, instinctive defender. It may benefit him if he is freed of the wing-back duty and can concentrate on being an attacking threat.
We don't play with out-and-out 'wide men'. Wing backs and a rotating front three seems to be the plan - 4-2-4 or even 4-4-2 don't seem to be on the cards any more. Out-and-out wingers? - no chance! Jahanbakhsh found that out (not that he was quite good enough anyway).