I think the 3 screw option is at least the same, but more likely both stiffer and stronger than 2 screws
Knowing that stiffness is "height" cubed, and strength is "height" squared, then if we say the bolts are a lot stiffer and stronger than the mast, a quick calculation say 0.5*0.5'0.5*2+1.2*1.2*1.2 = 2.0 for stiffness of the 3 bolt mast if bending the alumast just at the screw ends versus 1.0*1.0*1.0*2 = 2.0 for the 2 screw option, so same stiffness.
Strength is 0.5*0.5*2+1.2*1.2 = 1.9 versus 1.0*1.0*2 = 2.0 almost the same in terms of strength.
But as the screws are a lot less diameter eventhough stiffer material than alu, they will also bend and be weak, so they are 50 % stronger and stiffer with 3 screws, compared to 2 screws.
All in all the 3 screw solution would seem somewhat both stronger and stiffer IMO, at first glance and a fast mental approximate arithmetic calc.
Having said that, I prefer a 1 screw solution, riding so often and changing masts/boards a lot