So yeah: that Waltz is now called Blofeld only matters to the audience, and then only those who are up on their Bond history. To James, Franz may as well have changed his name to Phillip Blue Fuzzy Felt. It's an empty twist, made all the sillier when Bond actually starts calling him Blofeld in the final sequence in a bid by the screenwriters to try and make it feel more important. No element of the Blofeld reveal carries weight. We already know Oberhauser is being duplicitous by faking his death (and, really, that he killed Bond's second father figure is much more impactful than any self-given title) and that he's the movie's ultimate moustache-twirler. It doesn't make him any more menacing than he was before, it only makes you feel he should be because you know someone called Blofeld should be important (it's not like he actually does anything in the plot to necessitate such focus). Spectre has a reveal that does the inverse of the Blofeld reveal - the whole Max/C (another character who adopts a random nickname for flippant reason) is really working for Spectre - and while it too is incredibly obvious (Andrew Scott couldn't be more obviously evil in his introduction scene even if he wore devil horns), it at least has some bearing on the film's story and advances S.P.E.C.T.R.E.'s menace.
