Personal perception of a band can get in the way of an objective look at true marketability and actual numbers.
I don't think folks realize the intent of the tour with Kamelot. Dragonforce have sold more records in the U.S. than anyone else on the roster thanks to the explosion of Guitar Hero. Ultra Beatdown was a Top 20 record. They blew up in popularity and essentially skipped the underground club circuit as we know it. Do folks not remember their headlining tours previously in much larger venues than the current tour is currently booked with Kamelot? Hell, they played the Tabernacle in Atlanta previously (same venue that Dream Theater plays when they come through town).
The music scene is brutal. Dragonforce have had to adjust things once the fans that blew them up left them because they were never the true metal scene in the first place. This tour is allowing them to establish themselves back with the actual metal fans that were cynical of their mainstream success. It's a brilliant long-term strategy. The response on this tour seems to support that.