Yes, I do remember reading of Motobu's rivalry with Funakoshi. It might be in that article on this very site, about the "real Choki Motobu". Apparently Motobu was very critical of Funakoshi's style, saying it was ineffective and unrealistic. Motobu was known for getting into street fights in his younger days, and knocked out a Russian boxer when he (Motobu) was in his fifties. Funakoshi was seen as someone refined and scholarly. Obviously their approaches to training were different.
I agree, it is possible for descendants to surpass their ancestors in terms of skill and knowledge. How better to honor an ancestor than to take his knowledge and skill to a new level? Maybe in a culture that puts so much reverence in ancestors, it is a taboo to say that one is better than their masters were. Even if everyone knows it and believes it, out of courtesy one must never have the appearance of overstepping one's "place".