You don’t need a group to do delves and devles don’t havea timer.
But there are many who do not wish to carry a dead weight , so you are just lucky to find groups that you go afk with .
You kind of hurt your own argument here. This season, the easier dungeons are also the shorter ones. It’s impossible to separate out whether people like Dawnbreaker because it’s short, on the easier side, or both.
Then to go one step further, almost by definition, easier dungeons will trend to being shorter regardless what the timer is. Easier dungeons are more likely to allow you to 2 and 3 chest, which will result in a smaller time commitment. Shadowmoon Burial Ground in DF S1 had a longer timer than Algeth’ar Academy, but it was so much easier to get through that it was nearly impossible for the same group to spend more time in the former.
I think delves are the answer to your problem…
I don’t mind the 30-35 minute M+ dungeons. I did dislike the 40 minute dungeons like the new uldaman one. That just had so much trash in it that I felt they could have cut some of it out and been perfectly fine.