A lot of metal is recorded poorly, although over the last 10 years it has become uniformly much better. Goodness knows, albums like Destruction's Infernal Overkill, Exhorder's The Law and many other low-budget recordings are absolutely horrendous. However, a lot is recorded in a way that makes metal sound the way that genre of metal should. So I wouldn't necessarily classify that as a poor recording. The good stuff is recorded to a sound bands want to emphasize, moving things forward in the mix, EQ'ing certain frequencies and adding a multitude of effects. Sometimes a "cleaner" separation of instruments makes the music less "heavy". Less distortion cleans up the sound, but also makes it less heavy.
For instance, I always point to Exodus' Shovel Headed Kill Machine
as an "accurate" metal recording. It has well-defined separation of instruments. And while it is "heavy" and has great music, it doesn't have a brutally heavy sound.
It's kinda' like a woman with makeup. She adds all that stuff to make her look even better. And it works. Bands do the same. So while to most people this
probably sounds like a distorted mess fronted by a guy who was yelling too much at yesterday's football game, to me it sounds like it's supposed to sound.
I think non-metalheads can be so overwhelmed by the music that to them the recording sounds overloaded when it's actually their senses that are overloaded. I remember when I first heard Iron Maiden's Killers album decades ago and couldn't listen to it because I thought it was too fast. Now, when I listen to it, it sounds like granny driving her old Biscayne to church.
What I'm saying is that experienced metalheads know what they're expecting to hear. And if it reproduces that then it isn't a poor recording.