Sure, if you just look at Saudi Arabia at face value, its easy to say that it's a supporter of global extremism, but it's not really the case.
Saudi Arabia has been against extremist groups for awhile. bin Laden called for jihad against Saudi Arabia in the same fatwa he called for it against the United States. Saudi Arabia then revoked his citizenship.
And I don't know why you say they aren't fighting ISIS, the Saudi defense minister is the one who established a coalition of muslim countries to fight al-Qaeda, ISIS, and Hezbollah.
Further then that, Saudi-Arabian counter-terrorism has broken up terror plots targetting the U.S in the past.
Saudi Arabia may be an authoritarian shit-hole, but the authoritarianism does not stop when terrorism begins; the strong arm of their state grasps all.
Of course, that's for good reason. Even if Saudi Arabia is home to ultra-conservative Islam, it would have no interest in funding or supporting extremism; these groups threaten Saudi Arabian regional and national power.