Romans were still very strong. Nero, like Octavian was very cautios when it come to the Persians, so the war was just to keep a balance. A more decisive persian victory could've bloodier consequences, leading to an even quicker turn of roman tactics more aggressive (like Trajan style, more and more meaningless wars which in the end weaken both empires) or less ( This could lead to a more lasting peace, because the Parthians were not like the later Sassaninds and didn't want to conquer all the lands previously held by the Persians Kings and Romans could be happy to keep the euphrates and the desert as borders ( which are pretty good to defend)).