I use a 1080p monitor and what I’ve noticed is that once creators start uploading 4k content the 1080p version that I watch on fullscreen has more artifacting than when they only uploaded in 1080p.
Did you notice that as well?
Watching in 1440p on a 1080p monitor results in a much better image, to the detriment of theoretically less sharper image and a lot higher CPU usage.
No, that’s not what they are talking about. Even if you set the video to 1080p and make sure that YouTube isn’t lowering it to a lower resolution, it still won’t look very good.
Whether you notice or not depends on how perceptive you are, the quality of your eyesight and also the size and quality of your display. It’s hard to notice on a low-grade laptop screen (or smaller), as well as a cheap TN panel monitor, but go beyond around 20" and use a decent enough IPS panel and those blocky compression artifacts are hard to miss.