I think the issue some might be having has to do with biology and not "skill".
For instance, the idea that multiple monsters of a given type may all be different in their combat abilities/tactics/powers is an excellent idea. It really makes a lot of sense.
The problem comes when you start changing abilities that should be based purely on biology. The aforementioned Darkvision would fall into that category.
Not giving the PC version of a monster the same special "powers", sure, I'm fine with that. But saying that physically they must be different. That's where it becomes too much of a stretch unless its a one-time thing, not an every time thing.
"I want to play a Kobold"
"Okay, but you have to be hairy, and you don't have a tail."
"Whu-, why?"
"Well, because PC's are different from Monsters."
But honestly, there hasn't been too much of this in reality. There is no official PC write-up of the Kobold, the Minotaurs in the MM don't have the over-sized weapons, and the write-ups in the back of the MM do clearly say: "use at your own risk".
So really, it's not a problem until they start officially creating PC versions of monsters that radically depart from the baseline monster versions.