There's a difference between a model being perfect and a model being incorrect. I never claimed our current model was either. Our theories of the universe have been growing closer to the data we can attain over time, not further away. Our science is like an asymptote that never quite reaches perfect knowledge, as opposed to simply throwing a dart at a board and going "does this theory work? nope? welp," and throwing another one. It's the reason we still use newtonian physics despite having learned that, at a deeper level, quantum physics is the real deal. Conservation of energy has been central to every model for an incredibly long time, and there's never been any reason to doubt it, and nothing but evidence backing it.
According to a theorem within the realm of mathematics, Noether's theorem, any system that has a set of rules that stay constant over time, you have to have one variable that never changes. For the physics of our universe, they seem to be energy and momentum. Any set of rules you'd use to describe the universe, any possible model you come up with, would have to have some measurable property that stays constant. This is coming from pure logic, not scientific observation alone.
Some new physics model breaking conservation of mass is about as illogical as some new physics model revealing that gravity is a function of aetheric pressure.
If you have some sort of refutation of all of this beyond "well maybe in the future they'll know better", I'd be glad to listen, but I'm not really willing to continue debating against a person's faith.