Even then, you could probably set up an aim bot with a second computer using computer vision to detect characters, and sending inputs as a USB mouse.

This is true, but what is "reading and writing to memory" here? The article outlines dozens of ways of doing that with various hooks etc. And how they try to avoid that.

If I put a hardware connection to the memory (basically WIRES to my memory bus) then yes, it's very hard to detect. But that's also very hard and expensive to do...

It's cheaper and more accessible than ever to use DMA/hardware cheats from cheat vendors.

DMA cheats are only usable as many games aren't willing to pull-up their minimum requirements to play. IOMMU defeats DMA attacks. Secureboot (largely) solves pre-boot EFI related concerns.