H265 is more compressed than H264.
Hence requiring more compution power.
I have also noticed that the H265 files are not much smaller at times.
Most people don't really need 4K video at this point in time, let along have 4K TV's, or 4K monitors.
H264 compression scheme utilizes looking at a 16x16 pixel area, whereas a 265 compression scheme starts at a 16x16 and goes up to a 64x64 pixel area.
In the early days of digital I have witnessed analogue vs compressed video and the analog version looked much better, showing all the varied hues etc. So the less compressed should show color variations better.
Remember the Beta vs VHS debate. The Beta version was far superior, the VHS won out with longer recording times.