Some use the term "Supersoft AC" to describe a station like WDUV or WFEZ. I think even that could be a misnomer because such stations play very little in the way of "contemporary" music (which is exactly why I like such stations, so I view that as an asset in terms of my personal preference). "Gold-Based Soft AC" might be better, or other terms I've seen poking around certain sites include "Soft Oldies" and "Adult Gold." I think the appropriate term for such a format should make it clear that it plays little if any current music.
Otherwise it seems like the only thing that separates so-called "soft AC" from mainstream AC is that so-called "soft AC" stations play the occasional token Celine Dion, Gloria Estefan, or Michael Bolton song mixed in with the Elton John, Rod Stewart, Katy Perry and Lady Gaga.