CO2 forcing is a logarithmic function. There is not a 1 to 1 correspondence of CO2 concentration and heat trapping.Works in both directions. What's warmer? A clear night or a cloudy night? The consensus is that cloud feedback is almost certainly positive not negative overall.
So you acknowledge that CO2 DOES have a warming effect? What is the 1C based on? Seems pretty clear that climate sensitivity is significantly higher that 1C for a doubling of CO2. 180ppm => 280ppm is ~7C. There are other feedbacks in addition to water vapor such as albedo.
And when was CO2 concentration higher that it is today? It's higher now than it has been in ~10M years.