Things seems to have slowed down because AMD isn't competing, and Nvidia is delaying products. So the progressive loss of optimization is being slowed by the fact that drivers aren't moving on as fast as before.
It happened to CPUs before, now it's happening to GPUs too.
I actually read some article about this phenomenon a few months ago, it came to the conclusion that it indeed isn't as easy as it was ages ago to increase processing power of GPUs and CPUs. It may look like intel or nvidia are milking their customers when in fact we hit a technological plateau a while ago.
All we can do now is wait for smaller manufacturing processes so nvidia, amd and intel can cram up more transistors into their GPUs and CPUs. I also wouldn't expect too much of a PS5 in the near future, I would be surprised if it would have more horsepower than a non-Ti GTX 1080(perhaps even 1070). That's fine though, the bottleneck are the CPUs with consoles, let's hope AMD somehow figures out a way to build an APU with a powerful CPU.