That's what I was referring to when I said he's the star of one of the most praise-lauded games of all time. People rarely say anything bad about RE4. It wasn't the system seller Nintendo had hoped it would be because it was undercut by the PS2 version, but in terms of gaming history, RE4 is probably one of the top five games by measurement of review scores and relevancy in that generation of consoles.
Leon has actually been more present than Jill, however, in the last decade. Jill played a minor role in RE5, released in 2009, then starred in Revelations in the beginning of 2012. She was also a recurring support character in the Milla Jovovich movies.
Leon, on the other hand, was the cover star of RE6 in late 2012, the star of three Capcom-produced CGI movies, and stars in the upcoming RE2 Remake. The main thing going for Leon in this debate is that, unlike Jill and Chris, he's never been in a fighting game before. Which is honestly very surprising, and I think it tilts things in his favor.
That said, I personally don't even count Jill's appearance in MvC3. That wasn't Jill. That was an X-men character in disguise. She wasn't fun to play, had no personality, and I'm not a fan of the battlesuit. I want another MvC2 Jill. Very, very badly.