Majority of times bands that don't emphasize on brutality or heavyness have the best of those terms when they actually step into a more extreme direction. That's just my opinion. This goes for anything not just brutality or heaviness.
If you have a 40 minute cd with 4 blastbeats or 3 heavy parts those parts are going to be faster or more heavy than a band that is those things all the time.
That's how I see things when it comes to music. Not just heavyness but in general about organization and well placing parts to make them stand out like a sore thumb so they appear faster or brutal/ heavy or extreme and atmospheric,etc... in a general way. Five blastbeats on a cd will sound more faster than a cd that always has blastbeats regardless if the blastbeats were the same speed. This is in general regardless if it's blastbeats or heavy parts WHATEVER.
The ending to opeth 'a fair judgement' sounds more heavy and extreme than any texas death metal bands to my ears.