I disagree. You're conflating correlation and causation in a really weird way. Assuming that I've understood correctly, 60% plus of people play Eldar because that's how you win. It's not that people play Eldar because they're new and cool, it's because playing anything else means losing to Eldar, whereas playing Eldar means you might stand a chance of actually testing your skill against other players.
If u-boats were just being played just because they're popular and cool (on which I call BS, by the by, it's not like the Contracted Scout or even the JM5k was a popular ship people were demanding for ages before it dropped, it's not like it's been a staple of comics or it's featured in a current highly popular TV show or movie), they wouldn't be winning disproportionately - we'd see them throughout the lists, and we'd see a good mix of lists at high level, like we were before Wave 8 dropped. The Ghost is popular and cool (and among the best ships in the rebel meta right now) but you don't see it at top tables in anywhere enar the numbers you see u-boats and palpatine.
But we don't, we see more than 50% palp/aces and u-boats, because those are by and large more likely to make you win than any other list you could pick up and learn reasonably easily.
This DOES mean they're game-bendingly good. Not game-breaking, I never said that either. Meta-warping. They have warped the meta by being too powerful against certain lists which were part of a (mostly) balanced meta, but not against others.