I have experienced people that simply crushed me in swiss tournaments, they play like tigran petrosian for five straight swiss games with +95% accuracy, before and after the tournament they play according to their rating.
I also played people that feel underrated, probably because they keep losing 4-5 rating to people 100-150 rating points higher than themselves. I also experienced the opposite, people rated around 1650 that play like they have 100 points lower because they play a lot of games against people that are slightly weaker than themselves.
2000 in Rapid is not that impressive considering that I'm 2100+ OTB but I got to this rating by exclusively playing in Arena tournaments. I was nearing 2100 in rapid when I first started playing but then I lost a lot of games against cheaters and players who played much stronger than their rating. Because of this my rating then settled around 1800.
I eventually was able to grind my way back up to 2000 but it took me over 700 games to do so. Some players play WAY better than their rating and there are still of course a lot of cheaters (some of which are never caught). I think most players who play in Arena tournaments will notice how much stronger Arena players are compared to players of the same rating in the general population.
For example, when I was exclusively playing in Arena tournaments for my blitz games my blitz rating hovered around 1950. When I switched to playing in the normal 3|0 pool against players closer to my own rating I quickly shot up to 2100 within a few hours of playing. I'm guessing that I could probably get to 2200 and maybe even 2300 with some more grinding.
Anyway, I just thought I would share some of my thoughts and experiences on this topic. I would be interested to hear about other players' experiences with Arena tournaments as well.