Ori takes a lot of skill because she requires a very high level of micromanagement. Being able to position both her and her ball effectively takes a lot of practice and game knowledge. On top of that, being able to use her skills most effectively (who to w or e, or when to use them for damage or utility) takes lots of game knowledge.
All three of the champions you play have MORE kill pressure on her than SHE has on you, so if you're dying against her, you're straight up disrespecting her or getting outplayed. Additionally, she is weak to ganks because she has no escapes. Surviving a gank on Ori is all positioning, correct skill usage, and most importantly, how good you are at dodging skillshots.
Lastly, hitting a good ult on her can be quite difficult in a well organized teamfight. Typically, anything less than a 3-man ulti is a bust, and doubly so if you get no squishies. Unless your squishies just walk within range, getting into a position where she can ult them means she's putting herself in a position to get locked down and blown up by the frontline.
Edit: I'm a Mastery 7 Orianna player. I've been maining her for the past few months and almost exclusively play her when I play mid. While I consider myself better than most everyone I've seen play her at my elo level, I concede that I am mediocre with her. I still have trouble with max ball range, don't get the most out of her e, and have difficulty with certain matchups. She takes a LOT of practice to be even a competent Ori player.
or a simple 
against them, you deserve to get steamrolled by those 2.
