Yep, the "best" way to fight a super is by sniper fire. And laser designation for bigger ordinance. But we are right about having exoframes in real life, so in a "super" world the should have armored exoframes with .50 as the standard, and a 20mm auto cannon for larger targets with missile/drone support as well.
I think the first use for a bullpup .50 is for special op units as a sniper tool.