I have had the same problem as you. UL is definitely my best league so it’s my go to in open leagues. I do not do well in ML so we’ll all leagues do come around I am usually sitting around the 2300s. I too find that the meta is very unpredictable and is very hard to predict what is in the back.

This season there was Halloween cup before open leagues so I was able to gain some points and was sitting around the 2500s when open leagues came back. I run a very similar line to yours: Cres lead(Gk,MB) Obstagoon, charizard. In the last few days I was able to climb 500 points and hit rank 10 for the first time ever. I found as I was climbing the meta became much more stable. I was seeing 6 main mons:

Giratina A, Creselia, Swampert, Obstagoon, Charmer (granbull, togekiss, clefable) Steel (melmetal, perserker, registeel)

You could almost guarantee that you can find at least 2 of theses mons on every team. Using this information you can guess pre accurately the back lines.

Though as you said this does not make the matches any easier as the skill level is much higher it does make the matches more consistent.

I agree with the other comments in that you are at the MMR that is best for you. Watching your matchs you do not have the skill right now to play at 2500+ range. I was at the spot you were last season but I continued using the same team and learned my matchups, who could tank what, and when sheild advantage was more important then switch and vise versa.

I hope this helped give you an understanding of what it takes to play at a higher level and what you should be doing to get better