Wait, only a 2% brine? That's way too low for kraut. You need at least a 2.5% salt by weight of the cabbage itself, not just the water. No wonder it got mushy, that's basically inviting the wrong bugs to the party.
Oh wow, "total weight of cabbage and water" is a game changer. I always measured salt just for the cabbage weight too, like miam75 said. That explains a batch I had that just never tasted right, it was probably way under-salted. Doing the total weight makes so much sense because the salt's in the whole jar, not just on the veggies. I'm definitely trying it this way next time. Thanks for clearing that up!