Opening prep ruins my logic, help!

Whenever I try to play an opening after a very in-depth analysis of one of its main lines, I can't seem to get my stuff together if the opponent sidelines me! Like, I focus on the critical variation of a 1. d4 opening, but then I'm allowed to transpose into a fianchetto Pirc, and I feel so uncomfortable and planless that my brain just refuses to think logically, so I lose with relative ease.

For context, I know overmemorisation is one of the bigger mistakes at the beginner level, but currently I'm around 2000 on Lichess (rapid), and I don't seem to be able to get good results anymore merely by "following the basic opening principles". Getting outduped in the opening feels as bad as blundering the game away, and there are plenty o' dupers around 2000 and higher.

What I'm asking for is advice on how to "reset my thinking" after I've delved into very concrete variations. They take up so much of my memory that it feels like I have to choose between playing a good opening or playing a good rest of the game, never quite both if the opponent doesn't step right into my prep.

This tells me very little. I'd say that my style revolves around not giving my opponent control over the a1-h8 diagonal (for both sides), except if I can fully play around it, like in the Gurgenidze for Black.

But here's another thing: how do I know when I've overrated the control of said diagonal, and when not? Plus, you can, let's say, have such a cautious style that, at some point, all of your opponents are going to equalise against you so comfortably that you'll have to ask yourself if your repertoire itself is malarkey because you avoid the main lines like the plague.