We know nothing about Mikoto's abilities so nothing said in the OP holds any weight.
And Hagoromo didn't "praise" Kushina. He was just making a general point about talent not necessarily being passed on to your kids.
And we don't know what Hago said to Sasuke. For all we know he said something similar to Sasuke about this but in relation to having inherited his parents' natural talents.
Mikoto birthed two prodigies. It would be foolish to sleep on her just to wank Kushina.