If a bunch of people from my high school got in ED somewhere, does that really hurt my chances of getting into that school RD?
Depends on the school. If it is a larger school or a state school then probably not. Half my high school class applied to Umass Amherst and a good number of them got in.
No effect on your chances of admission anywhere. Some students like to believe this since it is a convenient excuse for being rejected.
If anything, it helps your chances; if a university has accepted this many of your school’s seniors ED, they must believe your school does a fairly good job preparing kids for college.