I totally agree with you. The tests are good ressources but the percentile does not have a real signification.
First of all, we can take the tests several times and then indirectly manipulate the percentile.
Second, if you compare the percentile of a guy who take the test some months ago and the percentile of the same guy who take the test today (with the same number of correct answers), we can consider a difference of 10 or 20%.
In fact it is just a result so it does not matter but the thing is, as you said, the percentile can have an impact on our moral.
So,
GMAT Club Tests are obviously very useful but I am not certain that the percentile play an important role in that. Moreover, it will be hard to correlate the result with GMAT prep Q score, just because
GMAT Club tests are not CAT. Consequently, IMO, the best thing to do is just to erase the percentile.