Such an unusual-looking vehicle, that MEMP.
Keep in mind that APB, Reborn, AR, etc. are partially restricted to the gameplay design present in the RTS games, and some of those RTS mechanics do not always translate to suitable FPS gameplay. This is why sometimes, some representation liberties are taken, and some deviation might occur here as well for the MEMP if FPS gameplay demanded it. As for APB's MAD Tank, I think you should bring that concern to Pushwall. I'm all-in for an improvement pass on niche-gameplay units.
W3D as an engine isn't at fault here, it's just design-level decisions/restrictions that can prevent niche-roles from shining. Gameplay-wise there honestly is not a lot W3D can NOT do (it is why I still enjoy working with this engine).