This point has probably been made already, but frankly, the only people who were promoting MGR as "the true DMC5" so fervously were the passionate anti-DmC crowd who just couldn't keep their outrage on check so they seemingly needed a game they could use to antagonize on the game. So they found MGR, a game they most likely never had any real interest on for what it was, but when they realized it was set to compete against DmC they supported it so passionately, along the way projecting their own wishful thinkings on the game, not to show "how much we like this game", but to show "how much we hate this other game".
If you ask me, scrutinizing every DmC supporter as a stupid, ignorant NT/Capcom/Temeem humper is just as bad as hating a MGR supporter as a hateful, elitist Platinum/Kamiya worshipper. Lots of people from both sides had irrational, dumb reasons for supporting what they supported and were equally bad at not being childish and picking up fights against people from the other band. Just like that, however, both sides had people with sensible, understandable reasons for deciding which game they wanted to support. Heck, and that's not even accounting for all the people who supported both nor those who didn't like either.
Point is, people keep making the same mistake: generalizing an entire side of an arguement and all of the people behind it, instead of discriminating particular cases between reasonable people with good reasons for their choice and unreasonable people who act passionately and don't even really know why they made their choice to begin with.
As for MGR, I'm fairly sure the kind of people who looked forward it mostly included:
a) Hack and slash fans who just didn't like DmC and chose MGR merely as an alternative to satisfy their wish for a good game of the genre
b) Hack and slash fans who did like DmC but also saw MGR as a good addition for their collection of games of the genre
c) Hack and slash fans who never cared less about DmC and simply looked forward to MGR for being a good entry to the genre
d) Fans of MGS who were intrigued by a new game of the series, but with different gameplay and focus on the story (a spin-off)
e) Gamers in general who saw the game announced, read about it, watched it and decided they wanted it, without having anything to do with the DmC issue.
And probably many other kind of people, but you get the idea.