Yes it is better if you have 2 midfielders they better be MCs... But even in 4-3N-3 and 4-3W-3 there are 3 Mcs so there is no danger in illegal formation unless you mean 4-2-1-2-1
4-3W-3 doesn't have 3 MCs...
FC Bristbury
Season 5, Level 5
League Winners Levels: 1, 2, 3 & 4
Champions League Winners Levels 2 & 3 Double X 2 (League and Champions League), Levels: 2 & 3