you definitely have to adjust your strategy to incorporate the pak43 into your unit roster. i almost always go fortifications in 2v2s now, and have had really good success with it. I always go for a very aggressive medic truck, and secure a large portion of the map with mg34s and a kubel. i place my pak43 next to the medic truck, so that if it gets hit by arty i can just reinforce, and sturmpioneers can just repair it quickly. its a very good unit to hold off allied armor until you can get your king tiger out.
And my B-4 fires twice, now no PAK-43 and no Medtruck.
I think the Pak-43 can be a good way to fight, under a few specific scenarios. Only if does soviets industry and towards heavy T-3. Any T-4, off-map or on-map artillery and all forms of static defences will melt away with little effort.