Looking at your stats, you have only played about 100 Rapid games. You mostly play Blitz. With blitz, it's kind of hard to improve unless you're playing Rapid as well from what I have heard. ( I don't honestly know, I barely play on this site anyways but I will usually play rapid when I do)
According to the majority of General Chess Discussion, however, Rapid ratings will usually be more accurate relative to how strong you are. Along with the added benefit of increasing calculation abilities and adding a bit more poison in your snakebite.
I used to play more Rapid, but there were a lot of engine users.
I only say this because I have gone on a 6-12 run sweep against opponents with both lower and higher rating than mine. Then, the very next day, I would lose about 6-10 games in a row, and the cycle repeats itself. No matter what, the system seems to be keeping me at a relative stand still in terms of stats. Maybe this is just me, I don't know.