The equation is $$$ X ability to capture $$$.

US is oversaturated with products, solutions, competitors, etc...

Where’s your evidence for that? It doesn’t seem to be the case based on the amount of US-focused start ups experiencing success that we often see on HN.

I’m currently building a product for the UK market, because like you say there is less competition. I won’t argue against that, but the fact remains that if my product were a success in the US market it would make more profit.

"if my product were a success in the US market it would make more profit."

The "If" in your statement is exactly my point.