The “mask” concept is not unprecedented in terms of canon material. I’m not sure about NEU’s stance on the topic, but the Revenge of the Sith novel features the following after Anakin disposes of Windu.

“And so the mask becomes the man,” he sighed with a hint of philosophical melancholy. “I shall miss the face of Palpatine, I think; but for our purpose, the face of Sidious will serve. Yes, it will serve.”

However, in the novelization, this goes hand in hand with the concept of being deformed by his own lightning reflected back at him.

And the circuit completed itself: the lightning reflected back to its source. Palpatine staggered, snarling, but the blistering energy that poured from his hands only intensified. He fed the power with his pain.

The yellow glare from Palpatine’s eyes spread outward through his flesh. His skin flowed like oil, as though the muscle beneath was burning away, as though even the bones of his skull were softening, were bending and bulging, deforming from the heat and pressure of his electric hatred.

In text, it does not come off as too “out there” (in my opinion) but in the film, it is not conveyed as well. This just supports HAL’s point that it all could have been portrayed better had the film actually set out to do so, rather than leaving it to supplementary material to go back in and patch up. With the available material in terms of footage, not much can be done.