Syria: 1000 Iranian Marines Join Russian Troops in Jablah Base
Don't know why you think this will be the full extent of military build up in Syria. You don't make this investment with the intent to lose your time, effort, and soldier's lives.
I mean... are you really wish casting them to lose the war because you... what, want ISIS to win? That is what is on the verge of happening. United States policy needs to be to help Russia / Iran / Syria / Anyone Else DESTROY ISIS. Syria should absolutely not be handed over to genocidal terrorism.
You think of this war as "house to house" and 100k troops, but that's not how it should be fought. That's how the US played policeman over in Iraq and that's how you lose a war. I can only hope that these military units take off the kid gloves and teach you what winning looks like. A real military leader will be there for killing the enemy, not playing policeman on the streets with their soldiers' lives.
ISIS is a mere militia, easily dispatched on the battlefield.
There is no excuse good enough for their continued existence.