There is a world of difference between going from 11.4GB to 6.6GB = 58% file size and 20GB to 5.2GB = 26% file size.
The N. Sane Trilogy runs @ 30fps and comes with 4k assets for the pro. The Switch won't run the game at 4k output.
The assumption that they got the game down to 26% of the original file size due to dialed down assets is much more reasonable than magic pixy compression.
Likening a legitimate technique used by lots of developers to something fanciful and not real is really quite derisive and you did it for no good reason other than to make your point seem more credible. Just wanted to point that out.
Also, Crash, like many other PS4 Pro games, does not feature native 4K assets. At best, the game offers 1440p assets (Vicarious Visions confirmed that was the case, BTW), which would assuredly not account for the 74% difference from 1080p, 900p or even 720p assets on Switch, so your point is moot in the first place.