1- First time I ever hear about this. Source?
google "lower resolution cpu intensive" im sure you will find thousands of hits, any tech site will tell you this in any of their tests for cpu and gpu components its commen knowledge, no offense.
Destiny 2 is also a good excample since its been in the news lately, higher resolutions on 30fps not a big deal because nativly it runs at 30fps but 60fps on 1080p is impossible, the gpu wouldn't need to do much extra work to render the extra frames but the cpu cannot sent the instructions to render the frames fast enough.
Sending instructions to handle higher resolution frames isn't as intensive as sending ADDITIONAL instructions.
Altough the GPU displays the graphics the CPU tells the GPU what to do.