What you conjecture about how the quiet eye works seems like a reasonable interpretation. But sounding feasible and being borne out by research aren't the same thing. There are studies where specifically longer gaze time at the ball is related to performance. This is from tennis but here's one study:
At least in one sport, staring at the ball longer improves performance until it bounces on your side of the court. This is tennis where there is less spin and the ball isn't hidden. If we were human computers that just needed snapshots of contact point to make quality receives, then quiet eye in this situation is somewhat irrelevant. But the results demonstrate that's not the case. That's kinda the whole point of quiet eye. It defies "common sense" assumptions about the specific sport. Stuff like "well I already know what the ball is going to do I've been a pro for 10 years" is proving to be no substitute for actually focusing on the ball.
If I would have to design a study to apply this to table tennis, I'd test how receiveing performance changes when the ball is always visible prior to contact point, versus very obscured (maybe over 50% of the way down) and only slightly obscured. Your conjecture is that all three would be the same and there is zero effect as long as contact point is visible. My guess is that the longer the ball is hidden, the more break there is in whatever benefits the quiet eye phenomenon is conferring, and more disruption to judgment.
Now is it significant impairment or minor impairment? I don't know. Even if it was only minor impairment, the fact would remain that players have been systematically breaking the rules by hiding the ball more to gain an advantage. If the rules say that only contact point should be visible then we can say that aspect of the game is part of table tennis. But the rules say ball must be visible at all times. So ball hiding is currently not a "skill" of table tennis and the rules already imply that there is an disadvantage to the server for partial hiding. So the burden is on those who believe it doesn't matter to prove that it doesn't cause any impairment.