I would never list my mare, she has a home for life here, but if I were going to, she'd be a 6 or a 7 on one of those scales. Or I would rank her as bombproof in the hands of an experienced rider.
She's about as close to bombproof+trustworthy as you can get, I even use her to teach little kids how to ride with very little concern about the kids falling off or having an unpleasant experience.
However, her bombproof-ness is a complete product of the level of trust she has with me, and her familiar surroundings. It's not to say that she's ever really "bad" but she is mostly blind so I'm something like her 'guide-human' and familiar surroundings give her confidence to move around as she normally would.
She's fine in a familiar area without me and she's fine if I'm with her in an unfamiliar area, but if I leave her somewhere unfamiliar or leave her with someone else, she goes quite a bit sideways. Even an unfamiliar person in her familiar pasture throws her off a bit. She's fine with it if I'm there, but she'd be impossible for a unfamliar person to catch if I wasn't right there [for me+someone, she'll stand there and not move a muscle - someone she doesn't know, it turns into a 'chase'].
It's not that she's bad, at all. Heck, I've never even come off her in the 5 years I've owned her! But for an inexperienced person, one that was unable to project the kind of confidence Lacey needs, Lacey could be quite scary. And that could go all kinds of bad ways - scared horse, scared human = bad wreck.