I think you are misreading the person you're replying to.
They aren't saying "everybody can be equally good at everything with practice."
They're saying "don't quit just because you aren't great on day 1."
First time playing basketball even if you've played soccer a ton and have good general athletic ability? Don't expect to hold your own if joining a game being played by people who play every week.
First time doing woodworking even if you have an electrical engineering background and the methodicalness is not foreign to you? Don't expect your first table to be stunning. Still gonna be bad at it compared to people with more practice!
Honestly, if you think you're great at something the first time you try it, you probably just don't know what being great at it actually looks like. (It could even be "similar result, but better in some hidden ways, and done in 1/10th the time.")
But if you believe that you'll get better at it with practice, you'll keep doing it.
If you believe "guess I just don't have innate ability here" you'll give up and never get good.