My 2009 RAV4 sport has the factory “Spray Guards”. I have considered mounting mud flaps to those, which saves me the trouble of drilling into any sheet metal.
Having driven a semi for over 35 years, I do know that a lot of spray is diverted by the flaps, as well as small stones being kicked up by the tires and the like. Sure, spray does get around the flaps, but having seen the occasional truck or trailer that is missing a flap, it would be a LOT worse without them!