Not too heavy that it becomes over-bearing, but heavy and if driven well, heavy and tight. I personally like heavy and tight. I like the bass on it. Upper-mids is a little bit too hot for my liking, but that's the only issue I have with it. I'm waiting on the K381 with smoother upper-mids and same bass.
I say heavy because there is good quantity of it, and it's north of neutral. So, is my heavy same as your heavy? Find out! lol
Regarding 50mm driver. You probably mean closed backs. HD800 has 50mm, but open with bass roll-off. Campfire Audio headphone is got much bass. This is too heavy. It's not like that.