Earlier quoted context omitted.
As long as games are running on user hardware/OS, you'll always deal with cheating. Server-side checks and computation can only go so far. For example: in competitive shooters (where cheaters are most prevalent) you can't have things appearing out of thin air. The client needs to know about things ahead of time to play sounds and to give other environmental hints.
I've always thought the line about whats cheating, and what's not is unfair and arbitrary. How is it ok that some players can play 4k 200fps and others 1080p at 30fps. The only way to be really fair is for everybody to Stream the game at the same res, frame rate and latency.
Some games do impose limits though, for example Overwatch doesn't allow you to use an aspect ratio larger than 16:9 and selecting a wider aspect ratio actually cuts down on your vertical field-of-view rather than granting you more horizontal field-of-view. This lessens the potential advantage of ultra-wide monitors.