Sorry, belatedly catching up here.
With all the recent research and new editions of Hoffmann, the role of Nicklausse (the Muse) has indeed gotten larger than it used to be. (The Met uses a "mixed" edition, largely the long-standard one but not entirely so.) Giulietta has always been the smallest role of the three "heroines," and remains so. I wouldn't think that anything special had been done to redistribute the roles to flatter this cast. It's just an oddly balanced opera in some ways.
I had planned to see the moviecast but was prevented by the East Coast snowfall. I did hear most of the radio broadcast, and thought that Calleja sounded marvelous, just as when I'd heard him live. The flicker of vibrato impresses me as a colorful and individual (and entirely healthy) part of his vocal color (just as I did with Troyanos).
The Marschallin is right in line with Fleming's roles in the last decade or so -- what the Germans call "youthful-dramatic" (or on the bigger side of "lyric"): Desdemona, Tchaikovsky's Tatiana, Rodelinda, Strauss's Arabella, Russalka. It's true that she has balanced these with roles sometimes sung by lighter voices (Violetta, Thais, etc.), as smart singers will generally try to do.