The issue stands mostly because we have no idea when people were/are using it and what type it is. MF was prime example.
Also, I think "penetration" Haki was a last minute asspull from Oda given his Luffy/Kaido comments in 2016. I think he always had the idea of FLOWING Haki, but this "penetration" crap was a last minute addition/extension because as he said he didn't want Luffy winning "just because his punch is too strong", so he divided flowing Haki into 2.
This was so ad hoc (just for Kaido), it's dumb... Now watch everyone and their mother hurt Kaido without penetration Haki, except Luffy.