Is a bullet bad for progress?

I believe blitz and bullet are just for fun, for real progress I think at least rapid games are best, 10-15 min minimum for real progress. Play some classic games, some tournaments, face to face, live.

If you are 2100 or up in bullet on Lichess, I'd say its good for progress in blitz and rapid (maybe if you are low on time in classical). But in general, I would say bullet has (unless you can play without getting your pieces captured in low time pressure) not many benefits unless you are just looking for a way for getting the best out of low time.

'I play way too much blitz chess. It rots the brain just as surely as alcohol.' - GM Nigel Short
Bullet is even worse.

Interesting quote

Spending too much time on bullet games at the expense of slower time controls might limit your ability to deeply analyze positions and understand the nuances of complex positions.

To each his or her own, but I don't see how blitz and bullet could help anyone improve. To improve, a person should first take the time to think about a position.

I personally think that classical games that are over 30 minutes are best for progress. It teaches and allows you to think for awhile and to consider every possible move and canidate move. Time pressure is also less rare and you genuenly feel like you deserved that win/loss instead of feeling que it was a cheap loss because you were in time trouble or that you only won because you were faster.

So many people here think of chess as a "level up" kind of game where you just grind away for a few months and automatically improve. It's not like that. To improve in chess you have to really want to improve, and that means you have to put in the work. That takes time. There are no shortcuts.

'Course a bullet is bad for progress, that could kill you.

Bullet can be a fun, help you think fast, develop fast tactics, however, its effectiveness for improvement depends on your goals and current skill level.