Yep--the point is that your tip does not depend upon the quality of your work.
Generally speaking, this is the general problem with meritocracy (which does not just involve tips).
Merit is evaluated with some metric, which almost always is biased.
So people being evaluated with an high metric are not really "better" than people getting a lower score.
And many people cheat, finding ways of getting an high score.
All this does not improve the real quality of work done.
Instead, on a general scale, it triggers opportunistic behaviour, unneeded competition where cooperation would be better, etc.
But the most annoying result, for me, is that those getting high scores in such distorted metric start thinking to be really better than their colleagues, and that the additional money they get is fully deserved.
I am currently rated very high in my work, but I am fully aware of NOT being better than my colleagues.
I am actually very lazy. I was much better and productive when I had half of my age.
But at the time my wage was 1/4 than now and I was considered not very good.
I adamantly admit that, when this terrible meritocracy was introduced, I worked towards getting an high score, dedicating time and effort to this task, which of course was subtracted to the real work.
It did take time to me for realizing how this game is wrong.
Apparently most people think it is fair to give a prize to the people performing above the average, and to punish people below the average.
This instead is profoundly wrong. It is an ethical trap.
But of course this is not really the place for explaining the hidden venom of meritocracy.
I am now fighting strongly against it.
But I feel that I am loosing the battle.
A few months ago our Ministry of Public Instruction was renamed "Ministry of Public Instruction and Merit".
So also our school system, traditionally very inclusive and "levelling", is now being converted in a meritocratic system, where resources will be concentrated on a small group of excellent students, condemning all others to subpar tuition.