Once you break the top shock nut loose there is no need to use the 9mm on top of the shock. While installing my Fox 2.0s I did not have to use a second wrench to hold the shaft in place, I was able to hold the shock body with my hand as I tightened the nut down and compressed the bushing. Also, the ratcheting wrenches really speed things up but make sure you have one with a swivel head
The shaft on my factory shocks would spin inside the outer body. It was rusty enough that even pretreating with pb-blaster, I had to hold it for quite a bit. and on the passenger side, it also helps hold the liner out of the way and didn't impede my use of a "gearwrench."
Swivel head probably helps but wasn't absolutely necessary if you don't mind the wrench handle banging/rubbing on the shock tower. FWIW Most of the fixed offset gear wrenches are 15° and might work except for the liner interference.
At this point, it's all hair splitting on how you do it - do what works best for you. I was just pointing out the tools needed.

