I don't understand why should the BW of the gain-boost opamp be smaller than the second pole(p2) of the main opamp. In my opinion if the BW of the gain-boost opamp is much larger than p2 , the doublet will be out of the closed-loop BW of the main opamp and also the gain-boost loop can be stable.
note that it is usually difficult to increase the BW of GB amp much higher than p2, it may require to bias the GB opamp at 1-2 order of magnitude higher current compared to the main opamp. And as you know no one likes to waste supply current!