Yeah, there is definitely some bass roll off but not more than with er4s. Otherwise the bass is definitely not lighter than the er4s - it's the other way around. Anyway, I don't really find it that lacking to bother me - you can always try a little bit of bass boost coz the N4 has surprisingly low distortion in comparison to iems like B2 or even er4s.
It's not a major issue imo, simply something I've picked up myself. I know the ambience with some tracks and could sense an absence in the low end at times.
I could play several tracks without any concern though every now and then some reach down low caught my ear.