If you make this argument about any single component, you end up with low performance across the whole system because it leads to a culture where everybody can point out that their code uses only a few percent of the CPU.
A valid point, as we should be frustrated that (in desktop computers, say) real user-facing performance hasn't been keeping pace with improvements in hardware.
Every decade, hardware performance skyrockets upward, but developers adopt libraries/frameworks/languages/low standards/habits which give rise to woefully inefficient software. It's so atrocious that it seems to roughly counterbalance the hardware advances. Heavyweight single-page web applications seem to be the endgame of this trend, for now.
See Wirth's law: What Intel giveth, Microsoft taketh away.
That said, the 80-20 rule is a real thing. It's possible that you'll get better real performance by writing 80% of your code in Python and the performance-critical 20% in carefully optimised C, than by spending the same amount of time writing it all in Java.
