...just bad basses.
I don't think ANY tone can be thought of as bad.
Sure, there are woofy, muddy, dead, boxy tones...but interestingly, most of these have their rightful place in at least SOMEONE'S music.
A lot of what people consider "vintage" tones, are what I'd call a "no tone" tone. Hofner beatle basses with flatwounds. Things that go "DUNT" in the night. No sustain.
Would I want that? Depends. Am I trying to do a "Jellyfish" kinda thing? A convincing early Beatles kinda vibe? A vintage sounding jingle session?
Ya get my drift? Even some of the "worst" tones can have their place, as they just might be historically or musically congruent to what you're trying to do.
Now, that said, a low quality instrument that hinders your ability to play it is no bargain. A bass that has a woofy, dark, or boxy tone when you're trying to sound like chris Squire isn't gonna help you either, and may send you off grumbling about your "CHEAP POS" bass...but sometimes the funkiest yard sale find is just exactly what the doctor ordered.
I remember when Danelectro stuff was considered ABSOLUTE JUNK. Made of friggin' pressboard (aka hardboard, masonite). Now it's "Vintage" gear and highly sought after. Who'da thunk it?
It may not be what you want, but just 'cause it's cheesy, funky and cheap, doesn't mean that someone, somewhere doesn't think it's the cat's @ss.