I've never seen a average % requirement except on some mentored cadet schemes they say at least 90% to continue in their course.
I read on here Ryanair want 88% but that's probably an application filter to get though thousands of applications. From all my friends at flight school most of us got at least 90% so there's no reason why airlines shouldn't expect someone to do their best as opposed to 75%.
"One man can do what another can do" is my motto.
I wouldn't worry about it though. Your average mark is over-rated and it's something a student pilot can use to see how well his efforts payed off. It's often used as a tool to wrongly judge other pilots on how great their skills are.
Believe it or not a fATPL I know said I wasn't good enough pilot because my average was 93 and he was better because he has 96. He wasn't joking either. I hope he stays unemployed the b*stard.