I would argue that a high quality, athletic central midfielder would fix basically all our problems (injury crisis notwithstanding).
I don't know exactly who (I liked the idea of Rice and Guimareas but neither happened) but if we can bring in some of that age the team for next year could be:
Ederson
Lewis, Akanji, Dias, Gvardiol
Rodri, new CM, Foden
Savio, Haaland, Doku
Say the new CM is 24 or 25, that's an average outfield age of 25.5 and we can start looking to phase out Bernardo, Stones and Kovacic as squad players, for the next generation.
The reasons we're struggling right now are i) no Rodri, best in the world ii) injury crisis and iii) severe lack of athleticism in midfield.
We've been pretty shite for the last month but the situation is far from irretrievable.