> we just came to with a convenient way to do calculations, slapped a name on it, and declared it a scientific law

Physics is a model after all. I don't think you are so far off. Lot of physics is predicated on it's ability to make predictions, and predictions often come in a form of calculation of something. There is even a saying "shut up and calculate" in physics. It is not without contention, but it does describe a lot of physics especially today.

It is also notable that you can have multiple different models about the same thing. Notoriously we have both lagrangian and newtonian mechanics, both which are valid but can be useful in different scenarios.