"Chinese who are currently leading have 2 billion people"

No, 1.2 to 1.3 billion.

"If we had over a billion people,is anyone suggesting that we would have won more gold medals?"

Of course. Sports is a big part of our culture which is what gives us the medals. With the same culture but a larger population, you would expect more medals.

Our medals per capita wouldn't increase in direct proportion though, since we're obviously good at some sports and bad at others. We'd saturate swimming, most team sports etc, but we still would be behind in athletics, gymnastics etc. To get twice as many medals we'd probally need 60-80 million.