My opinion: relating this setting to gearing/cassettes will cause way more confusion. Not only do many cyclists not understand gearing, but also: this analogy only works UPhill. Downhill it’s the opposite!
Set at 10% and you’ll have all the gears you need going up hill. And you also won’t spin out on descents, since it’s only giving you 10% of the gradient. So you feel like you have a wide cassette range on the climbs, and a narrow range on the descents.
Set at 100% and you’ll have to shift a lot on climbs, maybe even run out of gears. And you may spin out on the descents.
Gearing analogy just doesn’t work. I don’t understand why people always want to use it. And there’s no way Zwift would go for it!
“Gradient Feel” or “Trainer Realism” get my vote.