Actually “winning” the civil war is another matter. ISIL (Islamic State in Iraq and the Levant) appears, in the media at least, to be the most successful rebel faction. But that’s because ISIL is the most ruthless of dozens of rebel coalitions (or the government forces) involved. Moreover ISIL territorial gains have mainly been thinly populated desert in the west or depopulated (by years of fighting) areas in the north and central Syria. When it comes to actually controlling population ISIL is at a big disadvantage. The degree of savagery practiced by ISIL, especially against unarmed civilians who do not cooperate has made ISIL the group people are most likely to flee. Most other rebels and the Assads offer civilians benefits (economic and personal security) if they stick around. Not so ISIL which treats civilians like farm animals to be exploited and, if they are troublesome, killed. ISIL is the classic example of why Islamic radicalism has failed in reality (but never in theory or in the sermons of hard core clerics) for over a thousand years.
Islamists are just less-successful communists with a older holy book.