From research PD shines is grass/vegetation/mud. GT and MB are suited for the stumps more. 20/54 boat. Really 19/54 but I'm pointing the bow to get to 20 to avoid flotation. 3/16 bottom and 1/8 sides.
I'd like to hear whoever told you that explanation. You do understand that all surface drives use a surface piercing prop right? That means 1/2 the prop is in the water while 1/2 the prop is out of the water when you are on pad running. That means while on pad all the mudmotors with run stumps the same. If you look at the design of a MB and GT vs a PD you will see two that the out drives are at a 90 degree angle vs one with a 45 degree angle. You tell me which angle takes the worst impact from a direct stump impact.
Now if you had said you run hard bottoms the majority of the time and the design of the GT/MB shines there vs a PD I'd buy it. Saying one is better than the other in stumps tells me someone has run all 3 nor is familiar with the lower unit designs.
For stumps I'd make my decision on which one allows me to sit while driving so I don't get ejected from the the boat, which has less tiller torque, and which has the best customer service because at some point if you run stumps 100% of the time you are going to need service with any of them.