[com2kid]

Swings layout stuff was fine, better in 2004 than anything the web had until 2020 at least.

Also now nothing resembles native platform UIs, so that isn't a big deal. Swing was very theme-able, which is all anyone cares about now days.

[n4te]

Swing layout was bad then (gridbaglayout!) and is bad now. The framework's approach is bad. Components provide min, pref, max sizes that are very often just ignored. Components need a layout mystery object in order to participate. The mechanisms to measure and constrain components sizes and positions is bad. None of the layouts are sane and it's difficult to add your own. 95% of layouts are nonoverlapping components arranged in row and columns, but provided layouts do other things.

Swing was themeable but good luck if you ever try to do it. Customizing an existing theme is too hard. All components have opaque theme objects that are part of the complexity problem I mentioned and often hide functionality and parts you want to customize.

It's easy to shit on everything, but I really think UI could be done much better and that most or all toolkits make big mistakes that hurt productivity and cause a lot of suffering.