I don't see it that way at all. Perhaps I've been too immersed in this terminology (I built an ADU a couple of years ago), but it makes sense given typical property descriptions: it's a dwelling unit (i.e. a place where people live) that's secondary ("accessory") to the primary dwelling. Or is the depressing part the fact that it assumes single family residences?
'Dwelling' sounds deeply depressing to me - to 'dwell' somewhere sounds like to simply exist in a space rather than actually living and thriving there. To 'dwell' on a problem means to sit and think quietly. And 'unit' to me sounds cookie-cutter and impersonal. This is your unit, just like everyone else's. Sit in your assigned unit and dwell in silence, human.
I guess 'dwelling' and 'unit' don't have all those connotations to you?
Guess it comes down to your target audience. If you're market primarily consists of landlords looking to make rental income, ADU seems to fit the bill.
