No amount of R&D spending can bend the laws of physics to overcome the inherent limitations of silicon. I'm sure Intel also looked into alternative semiconductors (e.g., III-V) before giving up on the 10 GHz dream.
That a secretary typing a document or someone who only spends time on facebook doesn't notice the difference is irrelevant- consider, for example, the massive capital outlay by the financial industry to have servers located as closely to the world's trading hubs as possible. If they are willing to pay whatever it takes to shave milliseconds off a round trip, faster CPUs are a part of that equation.
I think the GP did not debate that but pointed out the for CPU speed/throughput, clock speed is only part of it. Adding functional units and allowing the CPU to process more instructions in parallel can have a big impact, so can e.g. larger cache, better branch prediction and so forth.
If you give people faster CPUs, they will cheer and find something to keep them busy. ;-) And for some people, there is no such thing as "fast enough". But for a fairly large share of desktop/mobile users, the is not the limiting factor as much as memory bandwidth and I/O.
Dude, Intel spends something like $80B/yr on R&D. This is closer to hitting fundamental laws of physics barriers.
They killed off their P4 line and developed their mobile line for a reason.
https://www.fool.com/investing/2017/02/05/intel-corporation-...
Surprisingly, power consumption also made huge impact. As tablets and laptops got more popular than desktop battery life became a major concern and thus TDP played major role in research.
Try this fun experiment: Underclock your CPU by half a GHz and see if you notice the difference in your day to day work.