Depends, if you take out the LBL arm on the prime and can dodge the SRMs its firepower is cut down alot.
The B is easy because its next to impossible to hit a sprinting Osiris with UAC10.
No one takes the C thank god, no way in hell you're beating that one.
Uller A was possible to fight in 0.3.2 if you took the gauss out first. However, with things slowed down it would be harder because he would get more shots at you. Havn't seen many myself.
The HL versions only work to 400m and take a while to do damage... so either farther off or really up close is your options.
A vet can easily hit the Osiris, but not so much in the same place if you can run around him correctly.
All that said, I fear the Owens C far more than any kitfox in the Osiris, its a big laser boat with epic armor and jesus speed, a big fapp you to the Osiris.