ROF wise, the JP4 and Stug are the best TDs in the game.
ROF for TD hardly means anything without penetration. Firefly has a garbage ROF but its still very usefull and powerfull TD simply because of its raw penetration, its less effective against medium armor while being effective against heavy targers.
Stug and JP4 have good ROF but very poor penetration, meaning that they are effective against medium targers, but they are slightly better then premium mediums against heavy targets. Stug is cheap counter to mediums, while JP4 is somewhat counter for allied TDs and mediums, but it hardly can be massed, so its more of a single support unit.
Point is being, when it comes to TDs axis do have problems vs heavy armor, since aside from AT walls, the only thing that can reliably fight heavy armor is panther.
Honestly I never understood this design, why would Axis get TDs which main goal is to couter mediums, while Axis objectively already has so many tools to counter mediums, while against heavyes they have no other reliable option but panther.
Not to mention that Allies can potentually get more heavy tanks and faster in general then Axis.