I think dissenters who left at the 1918 schism were much more influential than are generally thought of nowadays. Paul S L Johnson was one (mentioned in the original post). I used to have some of his books which he called the 'Epiphany Studies in the Scriptures'. Scanning thru them (didn't have the patience to read them all, as they are pretty dry and there are 17 volumes) I began to realize that there was an ongoing sparring between the WT at the time and Johnson. Johnson would publish an interpretation and the WT would print a rebuttal. Johnson founded the LHMM, which is still in existence and has a small following.
Likewise the ones who left and founded the other 'evil slave' organizations (like the Dawn) were influential in taking out at least half of the Bible Students of the time away from the WT. I don't remember all their names, but I remember A. I. Ritchie being one. During the 20's thru the 50's these people were the 'apostates' to watch out for.
These people and their movements are scarcely a threat now to the WT, but they left an indelible mark.