Actually, Assad was pretty much tolerating ISIS, and the Russkis only made a few token strikes against ISIS. The US backed Kurds did most of the heavy lifting against ISIS, which (ISIS) is down, but certainly not exterminated.
Given that ISIS and the rebels are virtually indistinguishable from each other, and that both are trying to overthrow the Syrian govt, and that both are a threat to Christians (while Assad protects Christians), you are full of bull feces claiming the opposite to be true.