If USA/Russia/China are the 3 most powerful countries, who are 4,5,6,7,8,9,10 ?

[palandio]

Or against Russia in Syria for that matter.

But seriously, what differentiates Afghanistan from Yemen is that the Taliban insurgency is mostly guerrilla warfare in rural areas of a country that has proven to be uncontrollable for any outside power.
The Houthi insurgency on the other hand controls major areas of Yemen including its capital and conquering these should in theory be mostly conventional warfare for Saudi&friends.
The difference between Syria and Yemen finally is that the Houthis have become isolated from the outside world logistically, whereas the rebels in Northwestern and Southern Syria can count on multiple outside supporters.

Overall the amount of power that the Middle Eastern regional powers (Turkey, Iran, Saudi Arabia, Israel) have is quite an interesting question and comparing them one against the other is quite worthwile. In the end I would probably include none of them among the top 10, but all of them among the top 20.