That’s a fair point; as you note, he primarily taught contact hitting, but as noted in the current thread “How has Baseball changed in the last 50 years?,” the 1970s and early '80s (when Lau was a hitting coach) was the era of large ballparks (many with Astroturf), where hitting for average was the standard of the day.
IMO, the big and lasting impact he had was in being one of the first coaches to champion photo and video analysis for analyzing and coaching hitting technique.
Regardless, even if the game is different now, he’s another good example of an outstanding coach, who had excellent results, despite being a very pedestrian player.