IIRC he also has a background in writing sourcebooks for pen & paper RPGs and his real talent is in nuts and bolts world building and if you look closely, that's reflected in his B5 scripts. While the plots and dialogue leaves a lot to be desired, there's a lot of detailed background information to be found. Indeed, I'm pretty sure it was DiTillio that wrote up the bible on most of the background aliens like the Drazi, Grome, pak'ma'ra, Hyach, Yolu etc.
Yes, he did. And I agree, there was a lot of world building in his scripts and that made the B5 univers richer than it might have been otherwise.
...also, I've always had a soft spot for GROPOS. If the guy that played Keffer actually had some acting chops, I think it would have been a whole lot better.
From what I gather, an *awful* lot of 'Keffer's' scenes ended up on the computer equivalent of the cutting room floor.