That's total bull-
. The Assad regime had a business relationship with ISIS and traded oil with it
http://www.businessinsider.com/revealed-the-oil-middleman-between-the-syrian-regime-and-isis-2015-3?IR=TAssad basically left ISIS alone for a long time hoping they would swallow up the Syrian opposition and the world would be left with the choice between him and ISIS, thus strengthening his position.
It's also extremely obnoxious to deny the very substantial effect that US airstrikes have had on ISIS. Nobody who actually pays attention to this conflict would deny that US airstrikes were
the fundamental element in turning the tide against ISIS. To this day, it is only with US close air support and weapons that the opposition Syrian Democratic Forces in northern Syria have rolled ISIS back, as have the Kurdish forces and the Iraqi Army.
To pretend that Assad who originally allowed ISIS to grow unhindered and did business deals with it is the only one doing anything about them is not just ignorant and factually wrong, it's quite puerile.