Can we surely agree that "bad overmapping" is that which detracts from the feel of a section, or otherwise makes it unreasonably hard or unexpected? These are all "subjective" in that some people enjoy them, but they're plenty objective if the mapper couldn't explain a deep connection with the music.
To clarify, see my sig, see those maps with pulse-crippling triples and see 'End Time'--a mapset which has one MP3 without sextuplets and then an [Insane] MP3 with them out of buttfuck nowhere. Nothing in the other diffs, the song until that point or the map's presentation implies them in the slightest. That's the crux of the problem, yet people will always find some way to weasel out of fixing that kind of error. This is why a strict, clear guideline would at least provide a basis to discourage this particular quirk.
May I also remind everybody that "the obvious" basically needs to be rammed down people's throats? It's as if some people don't use their brains when they map.