my uneducated opinion is that when you improve at chess you become bad at blitz, and the other way around.
Every time I make a realistic attempt (working at it) to raise my rapid / classical rating, abstaining from fast chess, I become horrible at Blitz within a few weeks...
When you are like "whatever I dont want to improve I just want to play", then you reach good blitz form within some weeks.
I can only imagine in the higher levels it could be something similar... imagine a GM or an IM who just -does not- play slow chess anymore, but has a rich experience of classical tournament chess in his past... after a year or two of playing mainly if not solely online Blitz, he will become a monster... on the other hand take someone like Fabi or Wesley, because they are pros they always have to keep working on classical, and therefore they don't reach this beast mode of online blitz... (where you can basically flag people down a queen if you are a nasty enough player)...
I think there are plenty of IM's and GM's who are completely retired from classical, and have no interest in further improving at real chess... so they naturally become insane at blitz
The problem with that theory is that Nakamura streams blitz all the time and is getting exceptional results in classic chess. If anything it's as if Nakamura's rating started increasing the moment he started streaming and playing blitz.
One mega genius dude dosen't make it the norm... I mean you know better than I do..
But I believe the fact Nakamura actually makes more than decent $ from streaming actually allows him to prepare for and play classical tourney in a way only he can... His mindset, and "litterally not caring", is quite unique, as the his results in classical don't affect his livelihood whatsover which critically removes a good % of the pressure... He has a good decade or more of being in the top 10 before he started streaming, too...
You're saying that because he's not financially dependent on classical it means he'll be better at it? That doesn't make a lot of sense to me.
They're all mega geniuses. You can't just look at the evidence of Nakamura and say oh well he doesn't count because he's a mega genius.
Not very compelling arguments.
He's a single case, but an undeniably interesting one.. He had a peak at around 27 years old or something like that and then like many started to fall downwards, barely remaining in the top 20 even for some time. Compare him with Caruana who plays a lot less blitz and Nakamura has improved much more than him in the past few years.
After he started developing his youtube and twitch career, which has a lot of streaming and blitz, it's like he found a new lease of life for his classical and 9 years later he's just 28 elo points shy of his all-time high.
Maybe he also devotes more time to classical in addition to blitz, that's quite possible. Noone's arguing blitz actually making him a better player, though you never know.
I think it's possible to conclude that moderate or even heavy amounts of blitz is NOT harmful to classical.
Blitz may be fun at times but it is silly to take it serious and should not be used to break ties. Rapid OK , blitz or heaven forbid using bullet no way! Just saw a game OTB where Magnus (already world champion) did not notice an enemy rook on the square directly in front of his king, had him in check. He ignored the check and made an illegal move. Bullet is about who has faster hands or reflexes. The best move seems to be the closet piece to your hand and or the clock. LOL