The system is the problem, not the players. Simeone kept juggling players since Costa's departure. Mandzukic didn't work, neither did Jackson, if a proven La Liga player like Gameiro doesn't work either, then we should pinpoint part of the blame to Cholo.
Personally I think that rivals are wising up to their system, ironically the way to stop them is bus parking, they can't create a lick when cholo field a defensive 4-4-2 (specially with 4 CMs like yesterday). I know that the 4-3-3 didn't work as he expected last season, and was used only as a countermeasure when 4-4-2 didn't work against the bigger sides, but they really need to adapt to a more attacking system if they want to stay in contention for the league. 4-4-2 should be only used when they play as underdogs or against suicidal attacking teams like Jemez's teams.