My understanding is that JetBrains puts a heroic amount of effort into making their Swing components not look terrible, and that they can do this because they're a well-resourced engineering-centric company whose main product is a GUI app whose users spend all day in it and often pay for it out of pocket. That Swing might be underrated for this use case (if you also need to ship cross-platform) is an intriguing possibility, but different from whether it's a good choice for the marginal GUI app.