People don't realize that you're allowed to tell LLMs/agents "no." In the real world, it's a professional faux pas to question the design of a creative coworker when you may not know design better, but LLMs/agents are not your coworkers.
Don't like abuse of serif fonts? "NEVER use serif fonts."
Don't like the gaudy color palettes? "Use this color palette with a white-dominant background"
Don't like the marketing fluff? "Remove all non-salient text from this app."
And there are a lot of designers who are good, but only in a different medium. Being able to make a good flyer, a good trade fair booth and a good website are completely different skills, but all too often the same designer is expected to do all of those, and more
I admit that those type of politics depend on workplace culture and I worked at two highly creative-oriented companies previously, and in both companies any attempt to point out issues in the design resulted in a "this is according to design spec; not fixing."
Don't like abuse of serif fonts? "NEVER use serif fonts."
Don't like the gaudy color palettes? "Use this color palette with a white-dominant background"
Don't like the marketing fluff? "Remove all non-salient text from this app."
You're encouraged to be picky.