This is where my mind went as well. It sounds as if you feel connected to the people in your group and want to continue participating now that you’re past the initiation piece, but you disagree with some of the initiation practices. If that’s the case, then working from within to shift the group’s culture seems like an excellent goal.
I would expect, though, that if you go in with an undifferentiated list of practices you disagree with, it will be harder to get traction than if you prioritize your list and identify what simple changes would move the needle in the right direction.
You mention, for example, that you felt pressured to drink (and to participate in distributing drinks to minors), but you acknowledge that no one was required to drink. So, maybe what’s needed is more explicit support for the non-drinking option, and you could be the person who was lacking during your initiation process, supporting and validating the sober path through the initiation process.
Asking the group to participate, voluntarily, in the anti-hazing training that exists for Greek/sports organizations, would also be a reasonable ask IMHO.
OTOH, I’d try to avoid getting lost in the weeds of complaining about things like pushups. (Though, as with the alcohol issue, you could certainly advocate for making modifications available - especially vis-a-vis acknowledging that all sorts of physical limitations and disabilities exist and could plausibly affect students who might join an a capella group, and therefore there should be forethought about what inclusion would look like.) Likewise, most people would weather the “blindfolded and locked in a closet” experience without undue distress, but then again, what if someone is claustrophobic or has past trauma that would make that experience harmful for them? Posing the question of “how can we be trauma-informed” rather than taking a rigid stance of “This is 100% wrong for everyone” might make more headway.
I think you’ll find that practically every setting in college (short of very socially-conservative religious groups, etc.) will include some of the sort of shenanigans that are described here. You’re not likely to be able to eliminate this altogether, but you can definitely help to dilute the peer pressure by serving as an example and as an ally to those who want to say “no thanks” but need some support in doing so. Often that’s all it takes - just one “safe person” so that people who want to set a boundary for themselves don’t feel alone.