I agree with you here. Sometimes I feel like a trench from the MFLB gets me just as (if not more) medicated as a full oven in the pax.
Are the differences in efficiency the result of using conduction vs. convection?
I'm not sure what you mean here. Both the LB and the Pax are primarily conduction vapourizers. I keep telling people in this thread to read the MFLB Vaporpedia section on technique because a lot of it applies to the Pax. The Pax does have a larger secondary convection component but it is missing the LB's infrared component. I have no idea how they all balance out, but the important point is that both of them depend primarily on conduction. That means: fine grind, slow draw. Dry material is key too, but that's true for almost every vape.
Most people don't grasp how gently and slowly you should draw, this is why they complain about a hard pull. The Pax is designed for a gentle pull. Pulling hard on your Pax is counterproductive, and if you're used to a convection vapourizer or combustion, then when you think you're pulling slowly and gently, pull even more slowly and gently.
As for efficiency, the LB has instant heat-up and cool-down and performs quite well with as little as you want to use in it. The Pax wants a full oven (twice the size of a trench at least) and has a standby heating mode. Even though the temperature is supposedly below vapourizing temps, vapourization is not a binary process. A percentage of some components, particularly the terpenoids that provide flavour, is released well below the magic temperatures you see posted in charts around the net. The Pax by its nature is more difficult to use efficiently.