Just make it clear to him that you won’t troubleshoot any of his issues if he still opts for Intel given the amount of evidence regarding issues. My father wanted to buy iPhone a few years back, I told this statement to him 
Also extra producitivity performance of Intel i5 14600KF is useless as gaming performance is what will matter. Heck my old i5 12400 is more powerful than PS5 pro’s CPU, even with lower CPU core count.
If he’s set on Intel, build him i5 12400 rig maybe & save money. I recently upgraded GPU to 7900GRE in my i5 12400 rig, there’s a good amount of CPU bottleneck in CPU heavy games like CoD BO6 but mostly it is fine for sub 100fps gaming, getting close to 7800X3D + 7900GRE performance in games like Wukong. Acc. to CoD benchmark, my CPU can just push 130fps but GPU can push close to 180fps (I have a 170Hz monitor). 3080 is relatively weaker than 7900GRE, so it should be fine with i5 12400. Only a handful of games at 1440p might perform worse on i5 12400 + 3080 vs say R5 7600 + 3080 rig at 1440p.
