Sometimes I look at the questions I get on here, and on Tumblr, and I feel like a Professor in some University lecture being bombarded with questions from the floor. Why do all these things seem to need precise, numeric values attached to them? Do I have to show my working, my references? Is it that people really can't find any evidence of what I say in the canon, or can they just not be bothered even looking?
Well, now that's out of my system: Manga!Mamoru and Anime!Mamoru are pretty similar in the first arc/season. The biggest difference there is probably their age gap - in the manga, Mamoru is just a highschool student, and only a couple of years older than Usagi; in the Anime, he's a university student, bumping their age gap up to at LEAST 5 years. This puts a few of their similar actions across mediums in different lights. When you consider how often Manga!Mamoru teases Usagi, and his "not even thinking of the consequences" quest to find the Silver Crystal, it seems more like a hormone-driven, not-very-world-wise teenager's actions. In the Manga, that same behaviour coming from a college student is... well, a little stranger.
But it's not until the later seasons/arcs that the gap between their personalities really becomes apparent. You mentioned that his personality was "nerfed" in the Anime, which is largely because Mamoru himself was "nerfed". He was just never there. In the first season, and much of R, Mamoru was in practically every episode. As the show went on, episodes would go by before an appearance from him as anything more than a guy who showed up at the last second, threw a rose, and ran off again: By the end of SuperS, he hardly showed up at all. He was reduced to basically a prop with lines. The few times he did show up, his role was as a painfully stiff, boring "foil" to Usagi - telling her to study, rebuffing her romantic advances, or just outright criticising her.
Compare that to Manga!Mamoru, who, on top of remaining a main character all the way up until the Sailor Stars Arc (he played an enormous part in the Dreams Arc [the Manga equivalent of SuperS] as a matter of fact), maintained much of his original passionate, "teasing" personality. When Usagi was in doubt, he would comfort and support her, rather than chastise her. Like Usagi, he matured as the series went on and he grew older, but he still had a lot of his original "spark". Far from the overly-serious, over-aged young man who hesitated to even kiss Usagi (even when they were alone), the two have rolled about on the floor in each others' embrace on more than one occasion in the Manga.
There are plenty of more specific examples, but this is long enough as it is. Hope that answered your question to your satisfaction.