And our perception of what it's neutral and what's not depends on which is our reference. My neutral bass reference is the R-50 for now. Maybe when I try a really neutral headphone I'll adapt myself and see that the R-50 bass isn't that neutral as I thought.
So for now I find them a little bass light and bright, but that's just my opinion.
I don't know if I made myself clear xD
Sure! You made yourself clear. Which IEMs do you have with the same amount of treble that you don't find fatiguing? With some recordings, the very upper mids where female vocals stand, sound somewhat harsh. But, with most recordings everything sounds smooth. However, I never listen at high volume for long. At high volume, there might be more recordings where the female vocals would sound shouty.
Which instruments or voices sound fatiguing to you?
My neutral bass reference are also the R-50. I also find them bass light with a few recordings. However, when I am in basshead mode, the R-50 bass is obviously insufficient. I have a grateful soul, which makes me appreciate variety in life.