That is too general a statement because with the correct EMS on a totally stock MSP, I can find you 20 more HP just by tuning the ignition more aggressive
Running the 9:1 vs the 8.5:1 means that yes there is more bottom end torque, but to say that he can make more with less boost is a bit misleading.
What he saves on reliability and safety is really big
He should run 9:1 it is the correct choice for anything up to 14 psi on 91 and up.
If he were to go up higher, he would need 93 and start to pull timing. I don't, I can continue to run silly timing much later which means that the "More with Less" is in reality false.
I might pull 350whp at 16psi easily when he might never be able to tune past 290 with any margin of safety.