If it were just "Harry being Harry" -- mortal, fallible, flawed -- the Angel wouldn't have given Harry the slightest bit of discomfort. The Angels don't stop mortals from mortally screwing-up. The pain was a clear demonstration that, justified as his rage may have been, it wasn't just Harry being Harry; Harry was being influenced.
Under normal circumstances I would agree, however the murder of and dying in his arms of the woman he loved, wasn't normal. Harry's reaction actually was a very normal human one, extreme emotion, grief, anger, shock, freeze, flight, or fight. There was no thought process in his reaction, it was simply reaction. It was Harry, reacting as a normal human, except Harry isn't a normal human, he is a powerful wizard and Winter Knight.
And, I repeat a critical point: not one but two KotC's, 100% of the Swords in-play, were came to stop Harry; who was, in the end, merely a Knight of Faerie. Any one KotC could likely have stopped the Winterknight. Both of them hints more-than-gently at Denarian influence.
No, it was simply that it took that kind of power to stop a powerful wizard/Winter Knight who was in that moment a very upset human being who was reacting with understandably extreme grief and anger. When Murphy died, Harry simply lost it, nothing more, but when a powerful wizard/Winter Knight loses it, it takes the likes of two Holy Knights to first stop him from harming anyone in his state, then calm him. You see it at a football game, if a three hundred pound lineman loses it because a guy on the other team got in a cheap shot, it takes several other linemen to stop him, then calm him. It isn't something you normally see a quarterback or one of the smaller backs do, they just aren't physically strong enough to hold him back in that moment
I don't think malign influence upon Rudy allows Angels to act to stop Harry. I point again to the Squires invading Michael's home: those Squires certainly were under Nicodemus & Anduriel's influence; but the Angels still permitted the attack on Michael's home, and for Charity to be abducted.
It wasn't angels that stopped Harry in that moment, it was his very human friends who stopped him, true they were better equipped, but in the end it was his very human friends risking injury to stop their very upset, but powerful and dangerous friend from doing something he'd regret later, and in the end harm their cause.
I don't think it takes the whispers of a Shadow (or other supernatural influence) to explain any of shitty things Rudy does.
I don't think so either, in the end Rudy is an emotionally unstable person who is also in plain English, an asshole.