You've clearly never heard any decent pair of headphones.
They are definitely NOT good for mixing. They won't even run without batteries, which is used in the pre-amp to over compensate the low frequency and bass.
In case you forgot, you want accurate reproduction in mixing, not exaggeration.
Even just for casual listening I find these headphones aren't good unless you only listen to rap music. Any other genre and it will sound too bassy.
maybe your rooms need lil sound treatment then headphones are useful for listening for noises/click/pops that some speakers don't pick up it may sound good on your system but im pretty sure it wot sound as good on other systems because you hear it different on phones then monitorslol? you can mix on whatever you want as long as you are used to it. ive been producing on headphones and i get a cleaner master than my krk 8" rokits
Don't buy headphones to mix on. The left and right channels will sound more separated than they actually are. Get a pair of decent monitors and maybe a pair of Sennheiser hadphones as another source to listen to and check your mix.