Thermostat has ZERO to do with the boiling point guy. Stop while you’re ahead.

This is false. Antifreeze does more than let it not freeze. It lowers the freeze point and raises the boiling point. The cap pressure also raises boiling point but the coolant mix has a lot to do with it. Another thing antifreeze does is lubricate the water pump, and has anti corrosion properties to prevent rust and scale in the cooling system. Also coolant is another name for antifreeze.