Inferiority of middle eastern militaries in the ancient world?

[johnhughthom]

Trajan conquered western Parthia adding it to Rome, and placed a puppet king on the throne, making rest of Parthia his puppet.

He conquered the western part of the Parthian Empire, not Parthia. He didn't get anywhere near Parthia proper, but that's being pedantic I guess. And how long did this puppet rule? I suppose it comes down to the use of the word conquered, did Trajan defeat the Arsacids? Yes, of course he did. Did he conquer them? Certainly not. And even the defeat does not necessarily mean their troops were of poor quality, how many empires could cope with another large empire attacking, whilst in a civil war?