There absolutely is a correlation between muscular size and strength. That’s why lifting competitions have weight classes. Nobody who can “lift like Arnold” is small.
When someone is new to lifting that correlation is hard to observe because the jump from totally weak to general health is a huge increase in the percent of force produced. But at some point if you want to lift a heavier weight you have to be bigger.
Strength is max power per muscle cell. Someone of Same height deadlift 600 lb at 300lb is weaker than someone doing 500lb at 165lb.
The 300lb person can suck air into stomach more providing an air jack like effect (more pronounced in squatting)