IMHO what sets EMS apart is the much higher recruitment. When you workout voluntarily, you recruit muscle fibers according to Henneman’s principle: first less strong ST fibers, then stronger FT fibers, and up to 60 % of them at the same time, according to the literature. EMS instead recruits all fibers at the same time, and if you crank it high enough you get theoretically up to 100%.
I don’t know the answer regarding hypertrophy, but I guess the stimulation frequency for hypertrophy may be different than that for explosive force. I hope Charlie can help you here.