Or we could use our axis only friends terminology and replace 'fine' with 'underpowered' and 'fantastic' with 'op'.
SU-85 is no competition for JP4. JP got superior stats, optical stealth technology, much better scaling, MUCH better supportive AT that doesn't require specific tier to get and literally no teching cost if you open with med truck.
Had allies something of this caliber we'd be drown in tears within minutes of its release.
That being said, I don't believe either is OP or UP, JP4 is pretty amazing but SU-85 suffers from classic T4 problem-you get units that can be replaced with different units more effectively and earlier(or later if we want to use ISU instead of SU-85).
T4 overall doesn't perform well enough to appeal to anyone to get it.
JP4 has higher armor (irrelevant if they fire at each other, arguably the JP's armor advantage applies only to mediums and infantry at) while the St wins in rate of fire and mobility. Their penetration is nearly identical. The weakness of Soviet t4 is a different story, and so are their threats, but I wouldn't claim the JP4 has superior stats or abilities (focused sight vs camo is a different topic). Perhaps the SU could use an armor buff but this is thinness of allied armor in general.
So the allies have something with less armor (arguably irrelevant with their intended targets) but greater mobility and rate of fire. Yes,SU85 with more armor will drown us in axis tears.