Not so farfetched.
The seeds of ISIS was the disbanding of the Iraqi Army, throwing 300,000 mostly Sunni servicemen on the street.... with their weapons, including highly competent senior officers, while being discriminated by the Shiite Iraqi government.
Then, a few years after the 2003 invasion, General Petraeus funded and armed Sunni tribal militias in order to fight against Shiite militias, seen under the control of Iran. There were huge sums of money distributed, that were never accounted for.
Then, Saudi Arabia funded what was to become ISIS in order to overthrow Assad of Syria, with the help of Qatar. One reason was that Assad didn't play ball and didn't allow a gas pipeline going through his country from Qatar to Turkey. The other reason was that Assad is allied to Shiite Iran, and Iran (thanks to the US destroying the Iraqi state) has become a regional power and threatening Saudi Sunni/Salafist influence.
What does the CIA have to do with that? Their massive multi billion dollar surveillance apparatus could not have been unaware of the huge sums of Saudi money being transferred to Abu Bakr Al-Baghdadi, the Iraqi-Sunni terrorist they hired to overthrow Assad. Then there was blowback against US interests in Iraq, and against Saudi Arabia itself, as Abu-Bakr stated that there was no room for a king (King Salman) within a Kaliphate, and that Saudi-Arabia was next. Plus, the CIA facilitated transfer through covert means of weapons and Jihadists from Libya to Syria after the fall of Ghadaffi
The US has really been bombing ISIS half heartedly... they have merely been containing them from the Kurds, Jordan and Saudi Arabia, while destroying the Syrian infrastrucure, just like they did in Iraq in 2003. They have let ISIS make inroads into Iraq (took over half the country) and against Assad, even during the time when Syrian forces had been besieged for over a month in Palmyra by ISIS, that they eventually lost.
The Israelis are sharing intelligence and cooperating with Al-Qaida affiliate Jabhat Al-Nusra because they are fighting Assad from the Western side of Syria and also threatening Lebanon/Hezbollah. They have also been reported to have bombed Syrian targets in order to help Al-Nusra terrorists out of a jam. They also bombed and killed the Iranian general who was an advisor in Syria, based on Al-Nusra supplied intelligence. Druze rioters on the Golan Heights recently stopped and torched an IDF ambulance because it was carrying wounded Al-Nusra terrorists.
It really boils down to the fact that the US isn't really concerned that Isamic fanatics will take over Syria after Assad falls (there is really nobody else, the FSA now being irrelevant), but what influence they will have on them (carrot or the stick.... plus Saudi appeasement money).
Now, the US is furious at Iraq for having set up a joint Iraqi-Iranian-Syrian-Russian intelligence sharing and coordination centre in Baghdad, led by Russian officers using Russian Command-Control-Communications-Surveillance sytems. That led to Iraqi forces recently destroying an ISIL convoy containing high value assets.