I used to work at an OEM that did this. When the VW Emissions Scandal was publicized, we removed almost every piece of code that did things like these from all our phones. Not sure if it was ever reverted eventually but performance test might not matter to HN users but it is something that typical consumers do look at when making purchasing decisions, based on our research.
Your second paragraph is completely ethically bankrupt. That a lie increases sales is at the top of the list of bad reasons to lie to customers (and they are all bad reasons).
It's nearly impossible to be "ethical" in large OEM companies because of the extreme competition and complexity of the organization. Most of these large OEMs are so political that even the smallest changes would require way too much effort.