Rapid rating about 200 points higher than Blitz rating. Is Rapid inflated or is Blitz deflated?

Let me start off by saying that I'm currently a solid 1800s player in the Rapid time setting, standing at 1816 at the time of writing. Earlier today, I have played several Rapid games, immediately followed by several Blitz games, in turn immediately followed by several Rapid games, and so on 3 or 4 times. For Rapid games, my time limit was 10 minutes with no increment, while for Blitz, it was 5 minutes + 5 seconds increment per move; in essence, the time control was practically identical for both Blitz and Rapid, as over the course of the average game spanning about 50 moves, each player would have accumulated about 9 minutes' worth of thinking time. In Blitz, I have mostly come up against opponents in the 1550-1650 range and significantly struggled - so much so, in fact, that I have dropped from almost 1700 right down to 1530 just today. On the other hand, in Rapid, I have played against opponents in the 1750-1900 range and beat most, raising my rating from 1775 at the start of the day to the 1816 that I have now.

Furthermore, I routinely check my opponents' Elos; indeed, it seems like my Blitz opponents and my Rapid opponents have almost identical ratings across the board - the 1550-1650 Blitz players most usually have rapid ratings of 1750-1900, while the 1750-1900 Rapid players often have Blitz ratings as low as 1450 (yes, even those who play Blitz just as much as they play Rapid). All of my friends in the same rating range as myself seem to follow the same trend.

All of this begs the question: is it that the Blitz ratings are too low (e.g. in comparison to FIDE or to chess.com ratings a few years ago) or that the Rapid ratings are too high? My initial instinct was the latter, given that the recent chess booms have brought in a lot of newer players who mostly play Rapid and thus significantly weaken the player pool. Furthermore, this hypothesis is lent credence by the fact that the 100th percentile in Rapid is equivalent to only about the 93rd/94th percentile in Blitz, suggesting a player pool strength disparity. However, having looked at the profiles of some FIDE- or USCF-rated players, it seems like it's the Rapid rating that's the closer match to officially-approved ratings such as the aforementioned FIDE or USCF. 

So what's the deal here, after all? Is my gut feeling correct, or are the chess.com Blitz ratings actually significantly deflated? If anybody has any information on the topic, please let me know, as I've been wondering about this confusing rating discrepancy for ages.

In comparison to Fide, both blitz and rapids are seemingly inflated. But in fact, I believe blitz is not inflated, but here we just have a larger pool of players, they play much more often, thus their rating is higher.

But rapid ratings are for sure inflated, even though currently my rapid and blitz are standing at the same level of 2250+ but, my rapid rating has a big rd since it’s being a long time I didn’t take it seriously (so with one win I gain around 20 points). If I face a 2200-2300 rapid player, it’s easier to win than blitz player.

Thank you for your reply; however, I don't think it's true that Blitz ratings are inflated. I have yet to find a sub-2200-elo player whose Blitz rating is within even 100 points of their FIDE, as usually their FIDE is much higher. 

Ratings only make sense relative to a specific pool of chess players... that pool of players who compete against each other to establish the rating ladder.

Unless the Rapid and Blitz pools include the SAME players, you cannot claim that either one is inflated. They rate you relative to DIFFERENT pools of players. You are comparing apples and oranges. Or perhaps apples and corkscrews.

I think I just play better when I have more time to think 

I'm the same. 1700 blitz player, 1900 rapid player (in 10+0). I think both ratings are inflated when compared to FIDE. But as someone commented above, you can't directly compare players/ratings across the different pools - but only to other players within the same pool.

I'd estimate a 1700 blitz player is approx 1500 FIDE. I know of a 1650 FIDE player who is 2000 in blitz. I think typically, people's blitz ratings are 200-300 points above their FIDE - with some people being closer, and some being further apart.

I dont think enough higher rated players play rapid for the rating pool to make much sense at the higher level. As you noted, a 1900 rapid player is in the top 0.5% !!! 

Personally, increment destroys my game, as I rely too much on flagging. Therefore 10+0 is easier for me than 5+5, and 3+0 is easier for me than 2+1, etc, despite the time controls being faster.

     You say that you only play 10-minute rapid games, but the chess.com system categorizes most anything at that time control or longer as rapid, so some of tour opponents' rapid ratings may have been influenced by longer games. Many players (myself included) play considerably better with more time to think, making their rapid ratings higher than blitz ratings. The fact that you played all your rapid games at the fastest allowable time control may have affected some of your opponents' play.

What you're saying makes a lot of sense, but I was looking for a comparison of real strength. And I think there has been research done which showed that chess.com Rapid ratings and FIDE ratings correspond almost exactly.

The research assumes you actively play in both I think

You cant compare rapid and blitz. They are both completely different.

As I explain in the original post, there is practically no difference between 5+5 and 10+0 (or 10+2, to make sure increment exists in both). You absolutely can compare them. As it turns out, below 2000, rapid ratings are consistently higher than blitz ratings - at the 1800 rapid level, the difference is around 150 points, on average. Moreover, 5+5 is an especially tough pool, increasing the difference even further.

At my current level, however, the opposite trend can be observed: rapid ratings are consistently lower than blitz ratings. At the 2500 blitz (my current rating) level, the difference appears to be around 100 points, so 2500 blitz is roughly equivalent to 2400 rapid. My current rapid rating is a bit lower than 2400 (2366 currently), but that's only because I've gotten so used to the 3+0 pacing that my time management in rapid isn't as effective.

5 + 5 ? 😅 are you joking, when one talks about blitz everybody assumes its 3/0 ones talking about.