When you put it that way ...
"+ Level" isn't on that list.
"trained only skill check" I don't know zip about to comment.
I vaguely recall a build circa pre-2004 that had a Negative AC to trigger all sorts of stuff.
Otto the Bugbear, was maybe the author, idk too hazy at this point ; clearly didn't catch on.
I do think the intentional Negative build part, is not something that non-informed would do.
Plus the part of a Level 1 + Skill N + Class ability, being better than Level 20 + Anti-Skill N
kinda keeps this at bay.