Airballs are definitely not something that all PotC's experience. However, I have personally seen balls that fly behind the ship (which is why I created the deflector because it was on my machine). It's also an issue that Stern was clearly aware of or else they would have never installed the sneeze guard. They definitely did not do that for giggles. At least I hope they wouldn't have such a sick sense of humor to install that hunk of nastiness.
That said, I'm not trying to sell anyone on the idea of having an airball deflector. They definitely work, and even if it only gives you peace of mind, great. If you don't want one, no problem, you may never see a PotC airball in your life and all is good with the world (well kinda, minus the whole year of 2020 thing...).