I think you'd find that people in general dislike percussive sounds, regardless of how loud they are (and basketballs are definitely percussive when bounced).
Tools like nail guns, hammer drills, jack hammers, etc bother everybody.
Pickleball is definitely highly percussive in nature.
Neighbours are seemingly far more tolerant of consistent, or droning sounds like lawn mowers, leaf blowers, pressure washers, etc even if those mechanical devices are technically far louder than a pickleball paddle.
People in general have little time for percussive sounds intruding into their homes, regardless of how technically loud they are.
Quantifying those loudness levels seems to be the only way the conversation can be moved forward to any degree though, so it's likely a good first step when considering that Pickleball appears as if it's not going anywhere anytime soon.