I think it's both: he was boring and bland, but that's exactly what made him an interesting match for Kira. I think he was a really dull character to watch on a TV show, but in the "reality" of their lives, would probably have been the most suitable long-term relationship of the men she was involved with, had he lived. It just makes for boring TV.
I've always suspected that the Bajoran men are boring on purpose, like it's a cultural thing. The women are all fiery and aggressive, and the men are all quiet and reserved. It seems pretty consistent. Of course Bareil has the whole monk thing going on which magnifies it, and his utter calm makes his romantic interest in Kira read as creepy.