IIRC, Walter Martin (Kingdom of the Cults) could not ultimately call Seventh Day Adventism a cult.
They are listed as one of the four major cults in the world in many Christian publications, but each person can decide for themselves. I was taught that by definition a cult is any religious sect that diminishes who Christ is. Since SDA’s are taught that Jesus is the Archangel Michael, they qualify. Not to mention they were found by a false prophetess, Ellen G. White, whose writings they give equal weight with the Scripture.