We do need a squad of approx. 25 players . By definition they cannot all get a game every week so you need to carry some players that can fill in when needed but accept not getting regular starts.
I think that we have a number of those in our squad at the moment but unfortunately they are getting games most every week.
Schneiderlin, Walcott, Keane, Sigurdsson would all be acceptable squad members to fill in when the first choice players are injured or suspended. They would get a number of games per season and would be coming in to fill a hole in a settled team . They would not be the strong men in the team and anything less than a committed performance would not be accepted from teammates never mind the manager or the fans.
I don't think we have a problem with the attitude of Digne, Minna, Holgate, Coleman, Davies, Richarlison, Bernard, DCL,Iwobi, Sidibe and maybe a couple of others. Their performances can be poor but I think their attitude is right.
I think we need a Roy Keane in our team where the half hearted performances we have seen would be called out there and then on the field. We may not be lucky enough to get another Roy Keane but there are leaders there and we need those in our team.