I'm a Spurs fan but I think I relate to what you guys are going through. The summer of 2013 when we used the Bale money to bring in Eriksen, Lamela, Chadli, Chiriches, Capoue, Paulinho and Soldado. Players of a similar age bracket who were thrown in at once and didn't gel.
Our team from the prior season was heavily dependent on Bale - in your case Lukaku - but defensively we were solid largely due to safety-first tactics. AvB tried to build a robust team but in doing so we lacked any flair and speed. Eriksen is top class now but at that time he was green and if you kept him under shackles we'd have no creative passer.
Then when our midfielders who only did one job well - protect the defence - lost form our slow CBs Dawson and Kaboul were exposed. Similar to you with Schneiderlin/Gana and Jagielka/Williams/Keane.
Squad building is the crucial part of moving up the ladder but when you need to shape a good blend of skillsets that compliment each other, not spend cash on the same type of player three/four/five times. We made that error and I feel so have you.