You'd think Nanoha would score more debate
I mean, you went all tongue-in-cheek but thinking about Nanoha is somehow fresher than thinking about Madoka (and thematic discussion sounds far better than going through Madoka minutae) sooo
A lot of this has to do with the themes. Nanoha makes its themes crystal clear, though it has some elements that people perceive as too dark for your typical MG anime (because they have normally never watched one[1]), the themes have some pretty key overlapping- friendship, redemption, a sense of justice for those wronged, and growing up, and all these themes are crystal clear. Like, when you really think about it, Shinbo clearly did have some experience with the genre before making Nanoha because with adult trappings he does hit on most of what makes a MG show what it is. But I digress.
Madoka's themes are far less clear cut, to the point that we debate what the themes are at all. Is it a feminist work in some sense? Is it a commentary on Japanese culture? Is it simply a cruel depiction of children suffering? Is it that idealism is pointless and there's no reason to try? Is it a deconstruction? Is it a subversion? Is it just a dark MG show? I've seen pretty much all these takes made (and similar ones), often times articulately argued and the arguers citing various points of the show and interviews (though who cares about those lol). And if you can't agree on the themes, you can't really establish any sort of moral clarity on the show itself and are going to have ridiculously different takes on what characters were right and who were wrong and who deserved what and what-have-you. Like your take on what you want to take from the show thematically is going to radically change your perception, so because you have far more different takes, you get far more argument.
Like, nobody would make a case that Precia and Jail were somehow right, and with Graham it's largely a handful of contrarians. Because Nanoha, even after Shinbo leaves the project, has clear themes and morals that as a result it tends to be super obvious who the good guys and bad guys are, whose actions are largely moral and whose aren't. And that's faaaaaaaaar from a bad thing, but it tends to lessen the degree of debate.[2]
1. I mean honestly it isn't as visceral as Precia in Season 1, but you could absolutely slot Hotaru's treatment in Sailor Moon S under "child abuse".
2. Though judging from the length of the Nanoha thread, somehow they manage to find something to argue about.