@DeepQZero If there's an obvious edit, i.e. if there's little ambiguity about what is being asked and you just want to clarify that or write it in a clearer way, yes, you can go ahead and edit the post yourself. If you want, in that case, you can also leave a comment asking the OP to make sure that your edit is fine - this is what I do.
In the case of the post we were just commenting on, I think many things were being asked, and, in that case, we can't just pick one of the questions (maybe the one that we like most) and remove the others. So, yes, as you understood, you should leave a comment on that post asking the OP to fix the post himself (and/or vote to close the most meanwhile, so that it doesn't generate poor answers)