Your are absolutely correct. Not just the SDAs but also the JWs and other cults. They lean on Ecclesiastes (and other OT passages about Sheol) and either ignore or twist the NT Scriptures which clearly teach that all the saints go to Heaven immediately, and are very much awake and alive in Heaven.Soul sleep is a Seventh Day Adventist teaching . . . and from cursory reading here I'm pretty sure that cultists abound.
The term "sleep" as a metaphor for death implies that when the body is laid in the grave, it gives the appearance of a person in repose and sleeping. But the soul and spirit are either in Hades (for the unsaved) or in Heaven (for the saints).