That's interesting as in my experience is exactly the other way about. It's the experienced developers that try to gold plate to avoid the issues that they had in the last project or two projects ago, whereas the juniors ship code quickly but unfortunately often incomplete and certainly lacking a reasonable amount of test coverage
I don't think the parent poster was saying that the learning itself was bad.
I think the gold plating they're referring to is a form of over-correcting. The learning itself is good, and correcting prior issues is good. But over-correcting and over-learning can be problematic and can lead to gold plating.
I don't think there's any easy indication of the line between the right-amount of correction and over-correction, but I don't think it's unreasonable to state that one can over-correct based on prior experiences.
The second-system effect is definitely real and is a trap most developers will fall into. I think gold plating introduces liability and it would be better to ship early. I am, however, conflating my own behavior and anecdotal observations to paint broad strokes.