Right now, the back line is the biggest issue as there are simply no alternatives. If Jags, Keane, or Baines is hurt, we can't stop anyone. With those 3 and JonJoe on the right, we should be able to keep it to no more than 1 against Watford.
But I agree with Davek for once. Although I don't think Ross is our savior, he can hold the ball and help tremendously in a team that was initially designed to play, direct, aggressive, one touch football. We've been KILLED on the counter because we cannot hold the ball. Beni seems great at it. Gana, eh, but he needs to be out there. Ross makes more sense with those guys stylistically. Ross's ability to hold the ball, while dismissed by Koeman, is needed for our plays to get forward. Yes, with a target man, that would help, but even without one, Ross can help tremendously.
That being said, I still think Sigurdsson is too good to not be key to any resurgance AND I think he can play well with Ross. Ross still wants to come back deep for the ball and hold the thing forever, but part of that reason is the lack of support he's had around him. Playing him with Sigurdsson would be perfect as Siggy doesn't want to hold the thing to begin with. Ross holding, playing it into Siggy and having him spring guys - Ross included - should be exactly how we generate our offense.
I personally would play Ross on the right though with Siggy in the middle and attack on that side 2/3s of the game. Ross would still be more inside to let JonJoe get outside and eventually Coleman. Unlike Baines, Jonjoe will actually push forward aggressively. Ross's ability to keep the ball enables that type of movement. Put someone active on the left - Lookman would be my choice - and Rooney up top. DCL just isn't the guy.
I also believe that a decent tactician can create chances and do well AT LEAST in midfield with a Siggy, Ross, Mirallas, Lookman, Vlasic, Davies, Klaassen, Gana, Morgan, Beni, Lennon. I'm sorry, that's WAY too many decent options to not be able to find 4 or 5 that can play well together. Way too many. With us being out of Europe, selling a few of these guys would be wise to buy a couple defenders. Because to me, the backline is the much bigger concern. No coach can solve that I don't think. Holgate and Williams can't play in the center. Just can't. Not even in a back 3. Baines hasn't been great going forward, but if he goes down, we've got no one out there.