Well there's math, and then there's physics math. Physics math is different. All the world is a frictionless plane, and we are merely spheres of uniform mass and charge density upon it.

You should see some of the calculus acrobatics they do in plasma physics. It's absolutely bonkers.

The fact that it's hard to know the inputs accurately and precisely doesn't make this any less of an equation. Given some inputs on one side, you get an output on the other. You might as well call y = mx + b an estimate.