I guess I'm mediocre in that it consistently seems to take me 8-10 hours to finish jobs that come with a 4 hour time estimate (my company is big on estimates). I'm also pretty sloppy - code reviewers routinely catch minor errors that I should have known better than to commit.
I have the experience, way too often, of using some feature that I pushed months or years ago and learning that it's, like, haunted or something. Doesn't work the way it's supposed to at all. Obvious failures that I should never have called "done".
When it comes to building a complete product, from start to finish, I mostly can't get past MVP stage (talking about personal projects in this case). And I once spent over a month trying to update the version of TinyMCE for a CMS that I was working on, and did not succeed. I literally got another job and left the company with that task unfinished. The new job pays double, and I still feel like a bit of a fraud.
And yeah, I'm writing "bog-standard PHP" as the other commenter put it. I've tried to get work in other languages to diversify my skillset, and haven't succeeded. At this point I'm starting to not care anymore - I like PHP just fine, loose typing be damned, and I'm starting to think I want to move out of technical roles rather than improve my language skills.