@harrisrat Glad to have you back! Yes, there is a danger in hinging arguments for theism on scientific theories that may be replaced in the future. I agree 100%. Though I think it is okay to tease out the implications of a scientific theory for our faith as long as it does not become a foundation of our faith. As an apologist, I think it is okay to note how a theory currently in vogue lends support to the faith - so long as we do not convey that it is our reason for believing. Do you agree?
You are correct that not all theories require equations. My understanding of my friends’ point is that when theories do require equations - as they often do in physics, which is built on mathematics - those equations allow us to accurately predict what happens, but they are not the thing itself.
For example, gravity. Yes, we know that throwing an apple causes it to come down and particles have an attractive force related to their mass. But ‘gravity’ is not anywhere - you cannot touch it, put it in a bottle or measure it. Gravity is a word we use to explain what we observe when the apple is pulled back down to the earth and F=ma allows us to predict the behavior of objects with different mass. But F=ma is not reality - it is a model of reality - a way of predicting behavior that has been observed.
Scientists observe reality and then seek to create a mathematical model that can allow them to predict the behavior they observe. But the mathematical model (F=ma) is not equivalent to the actual observation - the apple being drawn back to earth.
The Big Bang theory also has such mathematical models based on observations of cosmic microwave background radiation, etc.