You're right about mediocre researchers and their career satisfaction, and you're right to say that there's too many people pursuing research careers who shouldn't, but on the one hand you 're saying that some people are talented and special and on the other hand you're saying that the people who do well in life are those whose circumstances other than their talent (e.g. caring for a disabled child) enable them to make a valuable contribution to science.

So, someone who is talented and special, can nevertheless fail to make a valuable contribution because of their other circumstances. That's not life being unfair in handing out talent to everyone, that's the organisation of society being dysfunctional. Who knows what groundbreaking discoveries we are missing because the next Einstein or the next Darwin is a single mother of two living on benefits, in some inner city ghetto? If talent is not cultivated, it never yields fruit.

There's unfairness, and then there's the incompetence and pretentiousness of people who hold the keys to the treasury. I think the concern is mainly with the incompetence, and when people complain about unfairness, often it's the incompetence that really bothers them. After all, you can't do anything about unfairness, we really can't all be Albert fucking Einstein. But we should really be able to do a lot more about the incompetence that keeps most people from reaching their true potential.

Btw, I so disagree with you about what school results tell you about kids' talents, but that's another discussion I guess.