Weight does factor into the equation, but the definite trend, even amongst professionals would tend to be lighter than recreational riders is to go to wider tires.
And those 19mm tires, pumped to rcok hard only felt fast. We know have the data to know they actually are slower.
I used to TT on 18mm tires when I was young and didn't know better.
Your also getting a very small contact patch for cornering on a highly inflated 20mm tire.
And those 19mm tires from the old days were likely tubulars, not clinchers
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