The last couple of seasons have been built on having a compact back 6, with Bruno given the freedom to pull the strings in the hole, and a pacey front 3 getting onto lots of throughballs from Bruno's passes.
As difficult as it is to admit this, the wheels started to come off after Ronaldo joined. He necessitates a front 2. This means the manager either take bodies out of midfield or bodies out of the wide areas.
Under Ole, we pushed Bruno forward and took a body out of midfield. Under Rangnick, we've taken 2 bodies out of the flanks and put them into unnatural positions in the half space. In both situations, we've needed creativity from the back 6 to compensate for the lack of creators in other vital areas. But that doesn't suit the natural game of any of our back 6 players.
Since the back 6 has started getting tasked with doing more with the ball, they're getting increasingly pulled out of position (McFred got pulled out of position under Ole and Dalot/Telles are getting pulled out of position under Rangnick). That's at the heart of our defensive issues.
So what we have is a team needs to play to the strengths to our GOAT player, but a GOAT players who plays to the weaknesses of our squad.
The problem isn't insurmountable. But if we're sticking with Ronaldo, that'll mean spending big on CMs and WBs in the next couple of windows. Or else, dropping Ronaldo and going back to the counter-attacking 4231 that got us consecutive 3rd and 2nd place finishes in the last two seasons.