That's a perfectly good analogy.
You have an existing system architecture being given incremental upgrades over time. It will perform a lot better than the original, but that's not the same as a new system based on an architecture that are two decades ahead.
An Intel i7 - 975 processor, no matter how much you overclock and give it aftermarket coolers, is still not as good as the latest stock Intel i5 -9600k, despite its status as a flagship product at the time of introduction.
You are right that countries are not on par with each other in developing technologies, but you forget that countries advance at a different pace. UK was the largest and more advance industrial power than US in 1776. By 1876, that edge essentially fizzled. China is the largest industrial power on earth. Its higher education system produces 6 times the number of science and engineering graduates than US. It has more patent filings and published STEM researches than US. Twenty years ago China doesn't make Top 10 in the TOP500 supercomputer list. More than half the systems on that list is Chinese today.
I could go on, but I hope you get the picture.