Are there chess players for example, that have gotten to say, Lichess 2700+ Blitz online without ever playing OTB and then as soon as they started OTB, they were playing at a 2000 to master level?
Well, I'm not sure if there's anyone who has reached from 2000 OTB rating to master level by just playing blitz online. But there's an Indian player (V. Pranav) who used to play a lot of online blitz on chess.com. He was around
2300 in 2020 October and right now has around 2900 blitz rating. His highest being 3000.
After the lockdown got over in India, he started playing a few OTBs and managed to get his IM title. Earlier in 2020, he was around 2250 in classical and now he is almost 2500. You can check this out here.
V. Pranav became India's 75th GM on 8th August 2022.