I’d heard this before, but it’s a fun reminder of how, in a sense, the laws of physics depend on what size you are. (Or rather, which laws have the most impact depends on the size of objects in question)

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I'm not sure about this... for pure shear or tension load the strength scales by the square of the diameter, so increasing beam "linear size" by 10 gives only 100x strength, but our beam-bones would usually fail in bending, not in shear, where the strength scales by a factor of 10,000x (stress = (bending Moment x beam radius) / (Area Moment of Inertia of beam cross section), where the Area moment of inertia is a function of cross section diameter^4) And don't we already know that giant dinosaurs existed?

I don't know how convinced I am. First there were dinosaurs in the past, the brachiosaurus was 4 x as big as an elephant and there are probably yet undiscovered dinosaurs that were even bigger given discovery of partial fossils like the Sauroposeidon.

Also we know in the past there were dargonflys with wingspans greater than 2 feet and centipedes that grew as long as a car.

This seems like a flawed argument. By the logic in this article, wouldn't horses or cows, which weigh multiple times what a human does, have to have stocky rather than slender legs?