It is far more complicated than that.
It starts from the fact that US has been on a downward spiral and has been getting weaker every year. Even the colonies are recognizing this so they are increasing the pressure on US to get more benefit from being a colony. For example US hasn't sold any medium+ range weapons to any of them so they filled the gap with China, that angered US but they couldn't do anything about it!
I strongly disagree. It is just that US weapons have been grossly useless and it has been proven many times. For example when Yemenese attacked these Arabs none of the defenses that US had sold them worked. You are saying that the Arabs don't know how to use them but what about when the same people attacked US bases in Saudi Arabia and the same weapons operated by US military personnel protecting US military personnel also didn't work at all?
Well differences apart, USA military equipment is still most reliable and modern in the world far ahead of what China and Russia are producing. Gulf countries from day one have not focused on developing military themselves rather they still rely on USA for all there defense. USA is in every gulf country for there defense like Doha, Kuwait, KSA. You cant just have a strong defense by buying expensive weapons from west, it takes years of hard work and indigenization.