There is a huge variety of opinion among Seventh Day Adventists on the authority and relevance of the writings of Ellen White. Some hold it up almost like scripture and others don’t look to it at all, with every shade in between. I think the overall trend is away from adherence to Ellen White among Adventists.
By comparison there is little disagreement among JWs about the role and place of Charles Russell, to the extent that JWs are interested in the topic, they tend to accept whatever the latest Watchtower says on the subject. Which incidentally appears to be that Russell was not part of the faithful slave ans doesn’t have any clear role in Bible prophecy.