The thing about cosmology is that no one is really an expert. The biggest difference between a duffer and a PhD theoretical Physicist when it comes to cosmology is that the Physicist knows how to make his ideas sound sophisticated - he knows the language of his trade. But the ideas are only marginally more likely to be right.
Rather simplistic and naïve.
The difference between a duffer and a PhD theoretical Physicist is mathematics.
A theoretical Physicist cosmologist can test his theory with mathematical models. A sound cosmological theory will have a mathematical model that will confirm or disprove its possibility. If the mathematics determine that the theory is possible then a physical experiment can be designed to test the theory’s relationship to the real world.
A duffer would be hard pressed to design a mathematical model to demonstrate that the universe resides on the back of a turtle or any other theory he may dream up and be harder pressed to design an experiment to provide physical proof to backup that theory.
As a physics major I always looked at my major as trying to figure out the language of God....but I know what you mean there were always a few of “those types”.