Does Conqueror’s Haki ruin Zoro? No it doesn't.
Does being born a conqueror undermine all of Zoro’s hard work? No it doesn't.
Why? Because it just like what Rayleigh said, Haosoku Haki is only as strong as the user. So if anything, for Zoro to have a strong Haosoku Haki means that he's strong and that all of his struggles towards achieving his dreams has started to pay off.
Does being born a conqueror undermine all of Zoro’s hard work? No it doesn't.
Why? Because it just like what Rayleigh said, Haosoku Haki is only as strong as the user. So if anything, for Zoro to have a strong Haosoku Haki means that he's strong and that all of his struggles towards achieving his dreams has started to pay off.
For it to be worth anything in a combat scenario against vaguely similarly strong opponents it requires training. Even IF Zoro had conquerors from birth, without the training that he did he would have never been able to become the man he is today.
Even people that dislike Zoro having CoC should agree with that unless they legitimately think that Zoro was able to use Asura from birth without any training.