Conservation of energy is universally true given that you or i cannot travel at the speed of light.

Whereas supply and demand is obviously not universal and i'm not just talking about Giffen goods, Veblen goods or the Chivas Regal effect. No i'm talking specifically about ceteris paribus. Application of ceteris paribus is to step away from reality, the more you do it, the further away from reality you've gotten.

The model of supply and demand is useful and its utility is only reduced by ceteris paribus.

The law of supply and demand is blocked from existing, thanks specifically to ceteris paribus.

I was going to write that supply and demand is like a 'linearization' or some other regression around a point, but looking up "ceteris paribus" I'll have to thank you for forcing a good phrase upon me. :)

If something is universally true then it shouldn’t have to do with whether you or I can travel at the speed of light.

But beside that, you’re incorrect. Energy is not conserved in this universe. See e.g. https://www.preposterousuniverse.com/blog/2010/02/22/energy-... for an explanation.