My belief is that the main problem is our midfield.
Bereft of pace, passing and dribbling ability. It needs a complete overhaul.
If we assume a 4-3-3 formation I can see a front 3 of Walcott, Lookman and Tosun/Niasse/DCL being OK for next season.
Midfield 3 needs additions and replacements.
One deep laying player, one all energy and 1 creative seems to be the modern blend.
Energy can be Gueye/Davies, if we buy someone then the player at Lille, Bissouma, looks a good bet.
Creative I'd like to add someone like Zivkovic - 21 year old plays for Serbia and Benfica. Used to be a winger, now a centre mid. Great dribbler and gettable. Dowell could also play that role.
Deep laying player needs to be a playmaker not just a destroyer. Fred from Shaktar would be be first choice but not realistic. William Carvalho would be available, does the role but has limitations.
Genuinely don't see Klaassen, Schneiderlin or Sigurdsson fitting into the formation. The £60m they'd, hopefully, raise would cover he cost of those additions and make the team younger.