[caspar]

In addition to what other responders have said, another factor is that if you're a top (or better than average) performer in X, then the default assumption will be that you'll be a top (or better than average) performer in Y, given some time to ramp on Y.

That may or may not be true, of course, but it's an element in your favor either way!

(though fwiw, in my time as a past manager, I found that significant effort counted for a lot - it's cliche but folks who consistently put in extra effort and worked their butts off improved faster than those who relaxed, so they would soon exceed folks who relaxed, even if they had much less of a head start.)