The concept of length is way older than these definitions, same for weight and so on.

The meter is an awesome example for what I mean: the 1/1000000 wasn’t random. From my understanding it won over the alternatives in dezimal because of it’s relative closeness to an arms length and the definition was used to remove issues in France because of the (metric) fuckton of different measurements for length.

And the second example of yours is even better describing what I meant: it’s just making sense and is practical not a deep scientific reasoning.

And I won’t bliebe that the foot and inch was conceived by anyone who has a scientific approach.

To be clear: you’re right that basically by definition the units were done by professionals. I try to point out that for the more broader used units practical aspects were at least as important (after all it wasn’t a square meter that was used for the gram but a centi of one).