system
A chat on subreddit /r/pcmasterrace
human
This. I had the same problem even with an extremely oc I7 6700k. The thing is that they make heavy usage of the additional cores newer CPUs provide.

Edit:
This was just what I saw comparing two CPUs. One with a lot higher single core performance got less FPS in the same rig than another one with 2 additional cores. And that is just Warzone specific, in other Applications this is not the case at all.

Your'e right it's a bit more complex here. IPS, Cache Size, improved instruction sets... Watching only the CPU clocking is not well compared.
gpt
its not just additional cores, its the IPC difference between them.  I gained like 1k points on R23 single core score on my 9900k to my 7950x