Fair enough. But your point requires discussing nonetheless.
You seem to suggest that fontsize should adapt to width to fill the space (seemingly to a billboard, as per your example).
If the billboard technique was used on the web, I guess we might not have more than a handful of lines on screen (on a 16:10 or so). That would disable skimming on long texts and even more, barely display a single paragraph (that's a gut guessing).
Plus, and more importantly, the distance to the screen is such that a font too big is not more readable. There's a tradeoff to he found for the fontsize that not only has to take into account the size of the screen but also the distance of the reader from the medium.
I guess not.