> The gravitational force is the weakest of these four.
Isn't that distance dependent? At macroscopic distances, the weak and strong interactions are even weaker, no?
For the strong force the situation is the same in a sense, if you had a kg each of quarks of different colors — except you literally can’t have that, because the energy involved in separating a pair of quarks is so large that it actually causes two new quarks to snap into existence and pair off with the two you were trying to separate before you can separate them on anything approaching macroscopic scales [3]. So the strong force is obligatorily screened (camouflaged) at long distances, but only because it is so strong.
The kg-of-protons experiment on the other hand you could do in principle, it would just probably be better if you didn’t.
[0] https://www.feynmanlectures.caltech.edu/II_01.html
[1] https://sieste.wordpress.com/2012/04/22/feynmans-electric-fo...
What if you want to build a fusion reactor? For now neutrons have to be along for the ride but that's only because we can't squish and heat plain protons hard enough.
The EM force between a proton here and at the edge of the visible universe is the same as the gravitational force between two protons at 1000 meters distance. The scale difference in the "hierarchy problem" is truly not graspable by human intuition.
[This PDF](http://web.mit.edu/sahughes/www/8.022/lec01.pdf) starts with some potentially helpful context.
Usually this claim is discussed in connection to the so-called ["hierarchy problem"](https://en.wikipedia.org/wiki/Hierarchy_problem).