A lot, yes, but most is by no means inevitable. Half is also not inevitable. If you target a completion perentage at or below what players think is a fair expectation (say you require 50% participation and your survey suggests 90% of players find that upper bound fair), you're not gonna make 50% of people angry just because they get the content a little fast for their tastes. Missing content is also psychologically much more likely to create anger than knowing other people didn't have to play as much as you play.
Also, exhibit A is not a randomly selected sample, so it's not good scientific data about anything imo.
I have literally never seen anyone in Fortnite express anger that other people also finished the Battle Pass even though they spent less time playing and reached a much lower season level.
I have seen many many people angry about not having enough time to finish a pass in a game they like and played frequently.
The psychological reality of the problem makes is an extremely easy problem to avoid by survey in the vast majority of cases.
(I cannot prove that my anecdotal data is completely reliable in the context of passes, obviously, BUT it is well established scientific fact that people feel more fairness frustration when they are denied things that other people get than when other people also get the things they already have.)