If the predicted temperature nicrease was too large, then what needs to be adjusted? The CO2 assumption? No that was close to the actual amount forcing the climate. Not as much aerosol blocking effect? No, we now understand that aerosols had less cooling effect than previosly thought.
That leaves us with the climate sensitivity assumption - the most likely explanation is that has been overstated. By how much? Easy, by 0.8/0.5 = 60% overstated. Not 2.4 assumed but 2.4/1.6 = 1.5.
A scientist would summise the the climate sentivity was less than though and a figure of around 1.5 is more consistent with the data.
I have now concluded that you are no scientist.