Interestingly enough, sometimes I think Mildmay is more Mary-sue-ish than Felix. Physically, Felix is borderline Mary-Sue, but personality wise? No. He can be too much of a bastard. Plus, everyone does not love him, and those who don't love him, isn't because he's beautiful and they're jealous, rather because he can be a jerk. Every single traumatic thing in his past has actually shaped him. If he were a Mary Sue, he'd be perfectly wonderful, despite his horrible past. His past would make him ~tragic~. Or something.

Mildmay fits into some of the Mary Sue tropes. He's beautiful(according to Felix, and maybe innkeepers' daughters), but doesn't realize it. He has a scar that doesn't detract from his beauty(again according to Felix). He also had a tragic past, but he's still relatively a good person.

And that's when the resemblence to a Mary-sue ends.

I think it just comes down to Mildmay's not quite as developed(but not underdeveloped) as Felix. In the sense that because it's not really his story, he doesn't change through the story like Felix does. Since essentially, Mary-sue's are horribly underdeveloped characters, I think Mildmay is closer to a Mary-sue than Felix. He's not one of course. Just closer than Felix.

I completely adore Mildmay by the way. His voice is what captivated me in the series.