10+0 and 5+5 are not that different considering the total amount of time, but you might have to play under time pressure more often in 5+5, when you have play on the increment alone. Maybe you have a weakness there? The rating distributions in Blitz and Rapid are actually quite similar.
Rating in Rapid vs Blitz

At 1950, it says I’m in the top 0.4% of rapid players, whereas 1950 would barely make the top 40% on the FIDE distribution. So many players dilute the pool, I think it messes with the ratings. Also - not enough strong people play rapid, almost every top titled player is playing blitz and bullet almost exclusively. That must have an impact on rapid ratings too.

So 1000 Rapid is about 70th percentile on chess.com, but FIDE simply will not bother rating people below 1000. Of course 1950 is 60th percentile for FIDE! If they determine that you're below 1000, you won't even count as part of the population.
Anyway, those who actually keep track say that Rapid on chess.com is not that far off from FIDE, at least above 1450.
https://chessgoals.com/rating-comparison/#Chesscom_Rating_vs_FIDE_and_USCF
As for rapid vs. blitz, shorter time controls can have a huge impact on performance, particularly for newer players who just benefit from more time to think.

do not play rapid.i play blitz and bullet all the time. rapid is a timewaster because people stall and I end up losing points. i just focus on bullet and blitz.

Rapid ratings are easier than Blitz and Bullet at the lower levels, sometimes quite a bit. As you get above 1850 or so it changes and gets harder according to chessgoals.com/rating-comparison/
My problem is I am just starting to play, and playing rapid. I'm getting matched with players with a low rapid rating, like 1-400, but they have high Blitz and Bullet 1200+, so I am getting stomped pretty badly.
Why are opponents in Blitz so much harder than in Rapid? I play my 10 minute rapid games at the same pace as my 5|5 games, so I blunder at the same rate I think. What gives??