That's still not really a bottleneck... A Core 2 Duo & 1080 Ti would be a bottleneck because the 1080 Ti will likely never hit 100% usage due to the Core 2. Whereas the 8086K most certainly can, it depends on what games he plays. The CPU plays no part in 'limiting graphics performance' that's why CPU performance doesn't scale with resolution, it does however define maximum frame output capabilities. By your logic a Graphics Card is always going to be a bottleneck even with matched parts like an 8600K + 1070, because the 1070 will limit maximum performance in 99% of games compared to what an 8600K is capable of outputting, i just don't like calling it a bottleneck simply because a CPU has enough overhead to allow more, bottlenecking is used way too frequently these days when systems aren't very bottlencked, because by the nature of how bottlenecks work, either a CPU or GPU will ALWAYS be a bottleneck since no part is equally capable across the board. Also like saying your Monitor is a bottleneck because your 1080 can push 100 FPS in a game but the monitor is only 60 Hz, if you understand the analogy. Just my 2 cents on the issue.
As for RAM, 8GB should run fine but plenty of modern games benefit from 16GB. PUBG will push 9-10+GB easy, Star Citizen can max even 16GB systems, ARK usually up to 12GB, to name a few i've seen personally. 8GB is usually the minimum recommendation for games these days, with 16GB increasingly becoming the strong recommendation.