An announcement might have made you look better, but doesn't guarantee that another rider won't pull a U-turn while you're overtaking. I announce all my passes loud and clearly and still have people U-turn at the worst possible time.
I give people more time and space than what seems necessary, but my significant other gets impatient with the way I overtake on MUPs and blames other people for all the near misses she has. She's not wrong.