You say this like their viewers don't want long videos. They do. I am one of them. So if they started doing what you suggest, I'd stop watching them.
There is no sweet spot. Different people have different preferences. Not every Youtuber needs to make 10 minute videos. Not every Youtuber needs to make hour long videos. It depends on their audience.
If you don't like hour long videos, that's fine. You're not the intended audience. Stop trying to make every content creator abide by your preferences and just look for those who already cater to your preferences.
There is no sweet spot. Different people have different preferences. Not every Youtuber needs to make 10 minute videos. Not every Youtuber needs to make hour long videos. It depends on their audience.
If you don't like hour long videos, that's fine. You're not the intended audience. Stop trying to make every content creator abide by your preferences and just look for those who already cater to your preferences.