I have a suspicion that they might be better at a different job, too, Flying Dice. I guarantee you I'd be terrible in retail. As a lab assistant, I think I'm alright.
The problem with the idea that they may be better at a different job is that society may not value that job as much.
Let's use a hypothetical example with a person named bob
Bob does not have the work-ethic/intelligence/passion to become a lawyer, which means that he doesn't have access to a lawyer's salary.
But Bob has the work-ethic/intelligence/passion to become a garbage man. As a matter of fact, his skills and talents make him a great garbage man and so he gets a garbage man's salary.
Now Bob is leaving his apartment in order to get to work when he sees his neighbour Joe speed past him in the new Infinity he bought. Unlike Bob, Joe did have the work-ethic/intelligence/passion to become a lawyer so he gets to enjoy all the benefits a lawyer's salary brings. Meanwhile, Bob needs to take the subway.
Bob sees Joe and he thinks about all the things Joe has that he doesn't: a house, a large disposable income, fancy clothes, the ability to eat out at high quality restaurants, not having to fear paying for his children's college, etc.
On the other hand, Bob's life sucks. His living conditions are horrible, he barely has any free time because he has to work a second job to support his family, he can't afford healthy food so his nutrition is poor, and the future of his children are uncertain.
This right here is how modern society handles meritocracy in its purest and least corrupt form. The excellent live lives of pleasure and luxury while the mediocre struggle to survive. Now you may not have sympathy for Bob because you could argue that he deserved it (the only reason why he's in this position is because he isn't good enough to get a good job, let's assume Bob and Joe came from the same background for arguements sake), but the thing is, Bob is still performing an essential service that society needs to survive. It's just that his is valued a lot less. Even then, does any human being deserve to live like that?
And thus, I will state what I consider to be the biggest problem with meritocracy, "What do we do about the people who aren't good enough?"