IMO it's the general thing. F.e. for me the main thing that keeps COB out of the Melodic Death Metal tag (at least in the early days, now they're more thrashy) is the drumming, that has always been more powermetalesque. Even though he has the skills, Jaska's never used half of them for COB music. He does some fills and some beats, but never anything too extreme or too DM.
Now you can start flaming me and telling me that OMGNOOB COB ARE POWER METULZ N HAVE ALWAYS BEEN!!!11!!11!1!!1!!