Interesting. From a philosophical standpoint I see no quarrel. You could replace "physical" with "god" in your definition and it would read true to many religions. It's when dogmatism overrides doubt, questioning, and humility that people are misguided, in scientific theory and religion.
The difference is that the concept of physical minimally satisfies the required features to fill the conceptual role implied by science. If you replace physical with god, you are either eliminating the necessary properties of god or you're assuming more than is warranted.
"God, therefore, is the one most simple essence of the entire universe"
-Nicholas de Cusa
"We shall find God in everything alike, and find God always alike in everything."
-Meister Eckhart
"The superior devotee sees that God alone has become everything...He finds that everything, above and below, is filled with God."
-Ramakrishna
"In order to attain perfect union, we must divest ourselves of God...The common belief about God, that He is a great Taskmaster, whose function is to reward or punish, is cast out by perfect love; and in this sense the spiritual man does divest himself of God as conceived of by most people."
-Henry Suso
Materialism is essentially a philosophical stance, that everything in the world is physical. It's not something that is likely to be solved empirically and it's not clear how you would even prove it one way or another. Anything as-yet unexplained might yet yield to a physical explanation, and insofar as physics is well-understood, skeptics can retreat into talking about mental states and so on.