the equivalence resistance at the drain of M5 is much, much lower than 1/gm9 because of the feedback loop around M5 and M9. The pole at the drain of M5 located at very, very, very high frequency
Firstly, why do you think the voltage at the drain of M9 will increase by (gm*ro)^2 times ?
Secondly, why do you think Cgd of M5 will increase the same time ?
Show me the fomulas you used.