The Saudi Army is fairly well equipped. But it is small. And its competence is rather questionable. And most of their equipment comes from us. Remember the problems we caused for Iraq in 91 with computer equipment with hidden backdoors and viruses? You can be sure that we have such in what we have sold to the Saudis... And to add to the picture, I have no doubt that much like the Jihadis, we have hordes of informers within the ranks.
The Saudi military just isn't a threat to us. Their wealth is. KSA fully in the Osama camp would have more then enough cash to make AQ a nuclear power...
My point was not that the Saudi military is a threat to us....the problem is that there is no 'us' there except planes. I doubt the capacity of any Arab military (my experiences were with Egyptian, Lebanese and Kuwaiti). But KSA vs. UAE, Qatar etc is no contest...and that fight could cost us dearly. A little bit of (properly trained, meaning not host country) heavy firepower (say a TF with 2 armor and 2 mech teams) could probably defend at least our key assets in country...but there ain't even that. If the jihadis take over KSA, they could use the KSA military to very quickly take the rest of the oil sheikhdoms. And we do not have forces in place for that eventuality, and KSA is very unstable.