If you're joining a team that is expecting you to hit 80+ DPS uptimes then either A) You're trying to join teams that are above your 'paygrade' B) You're trying to join teams that are lead by wannabes C) You're self imposing demands through for lack of a better word, paranoia.
This is something you need to kick back and evaluate honestly with yourself, because frankly, your evaluation is total BS.
I won't bore you with an overly long story or so forth, but I can promise you first hand that most groups appreciate more than just big D DPS numbers on 'muh logs'.
Be friendly.
Be honest.
Be pragmatic.
Be focused.
Be reliable.
Be committed.
Those are the 6 things that I absolutely swear by. Have a look through my logs and see if you think I keep the company I do because of my DPS (I may well be a beast in dungeons, but I'm the first to admit that I'm pretty rubbish when it comes to my savage DPS, going on 20 years worth of healing habits are pretty hard to rewire), /spoiler, I don't. What I lack in skill and aggression, I try my best to make up for with practice and cunning.
In short, if you're not comfortable chasing 60-80% logs then simply don't. Either GTFO that SCH slot for starters or at least find a WHM that wants to push DPS and start pairing up with them instead. Having a main+off healer isn't the most efficient way forward, but in a casual or even midcore group that's just focusing on clears and farms, who cares? Mine didn't.
If you're expecting to get a static that is good enough to clear their progression in a week but isn't interested in numbers then I'm afraid you that you need to either sort your expectations out or 'get gud'.
Getting an A4S clear with my casual team was 2 months of graft, to see that as 2 months worth of screw ups is borderline insulting. Rather, I'd argue that was one of the most enjoyable progression pushes I've ever had in this game and I wouldn't change a thing about it.