No, it really isn't.
Saying The First Law of Thermodynamics "proves" that matter can't be created nor destroyed is wrong. The First Law doesn't "prove" anything, and it doesn't explain anything. It's an observation. That's ALL.
Actually, Physics is just an extension of process of observation.
This statement is objectively false. Physics is a branch of science which uses some observations in a specific way as part of its discipline. There is much more to it than that, and the act of systematically organizing, understanding, and predicting are far more important elements of the discipline than simple observation. These are what differentiates physics from sitting on your couch watching TV.
If I accepted physics as just an "extension of observation" [and I most certainly won't] I would have to say that Mayan astronomers were "physicists." No. They were not. They were just people taking some basic measurements and using them to decide when to plant or worship gods. That's not physics.
Einstein didn't magically come up with the theory of general and special relativity or the photovoltaic cell. His theories were based on a milenia of observations and theories such as Maxwell's equations, c is a constant in a vacuum, etc. Those theories were stepping stones. Maybe stepping stones in the wrong or imprecise direction such as Bohr's model of an atom but stepping stones just the same.
That is what classical and modern physics are all about. It is no different than when the theorists came up with the laws of thermodynamics.
Actually, and ironically both physics and thermodynamics share a very fundamental rule — matter and energy are not lost or disappear. All else is secondary.