Capitalism is also incompatible with meritocracy, otherwise how to explain that the children of rich people will have better education and socialization than the rest of the population? Do they have more merit simply because of the womb they came from? Are they better than an equally capable person born in an underprivileged neighborhood?
If you are better educated than I, you have probably developed skills that I couldn’t. This isn’t fair but it still matters; after a certain age it’s harder for anyone to benefit from my unrealized potential.
You're attacking a strawman. The person you're replying to didn't claim that rich people's children are more meritorious simply by birth. If we assume good faith (which we should), the other poster would similarly be opposed to nepotism which grants unfair advantages.