Mangini just doesn't handle dynamics well. His thing is being able to do single-handed drum rolls, playing ambidextrous, being stupid good with polyrhythms, etc. Beyond that, there's not much depth to his playing. That's probably why so many people think his drumming sounds no different than a drum machine, or programmed drums.
As far as the comment regarding his playing on The Shattered Fortress, I didn't really care for the overplaying he did during the mellow section. It just seemed really out of place, and too loud. Having said that, some of the other fills he added in the upbeat parts of the song were pretty sick.