Learning the gameplay is reading a related wikipage, which is acceptable. The hard/annoying part is learning UX. It really shouldn't be that complicated. Talking to people in adventure mode, managing jobs (as you said, dwarf therapist is practically a must since the base interface is just horrible), managing armies, hospitals... everything is a chore and you need a tutorial for everything. And every UX in game is different.

To dig for example. You have to create a designation for it. But how do you know that unless you watched a video/read a tutorial? On top of that if something is wrong, the game gives you very little clue. Do you have a dwarf with digging task? Is he available? Does he have pick? Can he pathfind? The game gives you no answer other than not initiating the digging (edit actually my bad, i think it gives you some logs for some cases.). Stuff like that is a hard barrier for most players and they won't be able to continue unless they are really committed.