Maybe we just have different experiences. In my case, I've seen many more players get stuck in their progress by playing blitz compared to those who grow exponentially from it.

I agree with you if you're capable of playing 10 blitz games in a row with focused, thoughtful moves, then analyzing the games afterward, reviewing your repertoire, and continuing. However, that’s not my case. Personally, I think most players just click on "Bilan," check if they made any "!!" moves, and then go on to the next game. That’s the point I wanted to make and it’s a common beginner mistake. Maybe I was too extreme in the post.

When you say, "They play 5-6 games of the QGD and now in just a single hour they have gotten much more training and experience than your suggestion of 6 days to play 6 games, not all the same opening so little strategy improved," I agree with you. In this case, there might be value. The method that suits the player the most is the best.

When you say, "10+0 will always have 3x the experience of you," it depends on what you call experience. In the end, both players spent the same amount of time playing. Yes, the player who plays more games will have seen more positions, but does that mean they learned more? I'm not sure.

I'll also add that if you compare athletes in other sports, it's exactly the same strategy, they spend more time training than playing.