I think that these things I've seen that are tells of a slop UI are when people without discernment (not as an insult!) don't do a pass over a UI. I'm working on a dumb little app to help me sequence photos for a book[0], and I'm building it with Claude (Opus 5.5, medium effort). The first pass was really sloppy, but I was surprised at how far I could get with some directed iterating.

This isn't a new problem; every generation of websites has tells of the lowest-barrier-of-entry tools of the trade. You could tell a Twitter Bootstrap UI from a mile away similarly.

The only difference I think is that AI will go ahead and add stuff that you didn't think of, like little badges and gradients and whatever. I think it's a different skill to say "no, this is distracting and unnecessary." The app I mentioned above has a few of these — extra stats about page counts and image counts and such.

[0]: https://photobook-sequencer.netlify.app/ (very much a work in progress, feedback welcome)