Alongside the too high brightness, part of the problem seems to be that the “glow/lensdirt” effect is also triggered when looking through the Ironsights by the tint itself.
Edit@Zesiir might be right about the new LMGs not being adjusted but the older guns are still too bright for practical use for me at night or in dark bunkers. (Aha the special KVM89 doesnt even have a tint yet) Here is comparison of a few different special weapons.