He's certainly influential, in that he's been a member and majority song writer for one of the largest Japanese bands in history and that his record label gave success to a generation of bands, some of whom became nearly as big, if not bigger, than his own band.
He's also certainly respected, as a musician via his classical work and collaberations (London Philharmonic Orchestra, World Expo Theme, Anniversary Concerto for the Japanese Emperor) and also as a producer for both his own music and that of others.
But do these really qaulify him as the king of Jrock on the whole?
Respected? Yes. Influential? Yes. King? No.