It’s just that single core performance sort of plateaued (as expected). We just can’t get it faster by 2x as we used to in a couple of years, and it is not real

It’s just that single core performance sort of plateaued (as expected). We just can’t get it faster by 2x as we used to in a couple of years, and it is not really perceptible otherwise, especially that most software besides artificial benchmarks won’t max out the computing capacity of CPUs, it’s mostly waiting for memory and IO. What we can increase is parallelism, but most problems simply can’t be parallelized for a good enough percentage of the workload, and Amdahl’s law can’t be circumvented. Nonetheless, many other things can be scaled, like resolution (like, think how much bigger 4k@120fps vs hd@60fps is), file sizes, etc, so the workload does increase and not everything can cancel out, hence the perceived slow down in certain cases.