Anyone can do work on their own car. It's not especially hard.
But a professional working on their own car knows tricks and has tools / ways of working that a regular person doesn't have access to.
You can tell the difference in the result if you know where to look.
Sometimes it matters: the way you change some components matters - and while you're there with half the engine bay cleared, you can fix a few other things that usually fail in this specific model.
Sometimes it doesn't: oil change is hard to fuck up, but not impossible.
The the things I've made with agents aren't hard to do for anyone, but I can claim that I can pick up any of my projects 6 months from now and confidently add features without worrying about stuff breaking or the agent doing crazy crap - because I build the limits into my projects by default.