You are describing standard Einsteinian relativity Big-Bang cosmology perfectly.
Flat-earth actually comports elegantly with virtually everything we see and observe.
even if that were true, which I doubt it is... by those standards, your cosmological model has led to a widespread conversion to atheism and agnosticism (and all its associate social and moral behaviors)
It could even be argued that a generation of education under the state education of your cosmological model led to boys and girls not knowing whether they're male or female. I don't know any flat-earthers without a healthy respect for commands God has ordained in nature like the male and female. But the "Science Rocks!" people frequently seem to struggle with basic realities like this. Am I wrong?
There is something about the idea that we came from billions of years of exploding stardust that makes people wonder if we had a creator at all.
Also, the Flat-Earth model, (generally speaking, i.e. Biblical cosmology), harmonizes beautifully with scripture. It's rewarding to simply believe that God did what he said he did.