What is the average gamer's tongue stamina or tongue dexterity like? How long do you have to practice to improve for this to actually be useful?

I feel like it's probably pretty hard to get good with this.

Some people have much stronger and more nimble tongues than others due to physical differences (e.g., tongue size, the length of the tongue frenulum, etc.). But this is the case for the hands as well, which is why people have different input preferences and different gameplay preferences.

Personally, I think I would prefer a mouth controller over a traditional controller. I am very prone to tendinitis in my hands, plus I have small hands and short fingers, and can't play twitchy games well because of it.

The picture of a tongue mouse from article (maybe it's a render I don't know) seems to have maybe 16 dpi so it is probably fits for secondary mouse just for rotating the world, but for tiny pixel-hunting I would like to have something with a multiplicator.

There is a streamer named RockyNoHands[0] He plays Warzone entirely with his mouth. His controller has tubes that he blows and sucks to control the character.

It is really impressive watching him live on such a competitive game.

[0] https://en.wikipedia.org/wiki/RockyNoHands