It's weird, because a lot of songs written to be an anime opening (Let Me Hear - FALILV) get extended versions later on. However, I think Inferno works perfectly at its current length. It's quick, to the point, and makes great use of its time.
They came up at the same time and played a lot of shows with them, so there's significant overlap in their fanbases. The "Similar Artists" list is just poorly named; "What Other Fans Listen To" works better.