"I play the way I want" -Randomperson

[Rubieus]

That they meet the min ilvl and behave in a manner that does not violate the ToS are the only things you can expect, that is correct. In this case "expert" is just the name assigned to that grouping of instances. There is no "skill level" parameter they can use to block people who don't meet said skill level from the queue.
If you have standards you expect others to meet that go beyond those defaults then you need to use the party finder.

I don't have a checklist of expectations when entering into a DF. What I do have is an expectation of player responsibility. If I am a tank, you would expect that I chose that role because I wish to hold aggro and get hit in the face alot. If I chose Healer, it means I prefer not to get hit in the face and will reward you with some form of healing should you prevent that from happening to me. That is the only expectation I have.

So regardless if you are Tank/Healer/DPS; your responsibility to the team is to do your job correctly. It doesn't have to be the best. But refusing to play your job as thedevelopers intended. Just makes the game harder for everyone else. You are right, there is no parameter for skill level. There should be. There should be some form of gauge like a Maat's Cap questline or solo guildheist questline that prevents you from ruining my gaming experience because you can't or refuse to play your class as Yoshi intended. Instead, you (again not you personally) wish to run around half naked as a tank trying to spam fire spells as a gladiator because you saw it in an anime and want to be like that guy? _-_ Cmon..

It's not called "DF Roulette expert mode" because you'll be placed with "expert" players.

I apologize, my sarcasm may have not been blatant enough.