>>Okay, here's a comparable thing. Same code running over the years: my solitaire game. Apart from some minor cosmetic issues, the code is mostly the same as it was in 2003. Shortened it by a third when adding jQuery in 2008, which actually made it slower, but looked better.
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>>And guess what, it's now blazingly fast. I can't even notice when it reshuffled the cards and laid them down again. And back then I could just about see when that happened, or when it had to do a double loop to check whether the game was over after the last move. Even on my clumsy Pine64 phone...

That's partly due to faster hardware, but mainly in improvements to JavaScript performance. When Google developed its V8 JS engine it improved JS performance by a lot - this source claims 10x: https://dri.es/a-history-of-javascript-across-the-stack . That forced all browsers to up their games.

That's similar to the performance gain going from dBASE III+ to FoxBASE - about 6x if memory serves.