Why nerfing something that is well balanced?
Maybe because the Altar, even after the changes to the damage nodes, will still give a huge chunk of damage boost. Also this is testing phase 2 before droping an actual theme on top of the perma Altar. So next season we will se more nerfs and buffs, maybe some of the changes reverted.
I generally only use Marauders when I play Hardcore because in case of a DC, a nearby turret is the only possible way kill mobs that are swarming a DC’d toon. But M6 is a slow play style and it takes a long time to get all five sentries to hit their targets. My guess is that the Altar will buff all builds and they wanted to push M6 down towards the other DH builds.
The problem is that there are no pushing DH builds. So players will focus on other top performing classes and builds and occasionally revisit DH, and possibly M6, from time to time. It’s not efficient, but it is nostalgic.