The two basic factors that deprived the Russian intervention of success in defeating the rebellion are that the quality of the pro-Assad ground troops isn't very good and then this one of particular interest to me:
Second, the regime’s biggest problem seems to be manpower. Hard numbers are nearly impossible to come by, but anecdotal reports and battle footage indicate the number of fighters involved in any battle at one time is low, regardless of its importance. The Aleppo siege was broken by no more than 4,000 fighters, according to my conversations with members of the opposition. Opposition sources report that the assault in Hama province reportedly involves no more than 2,500 insurgents, facing regime forces in the low thousands despite the province’s strategic value. Footage of some of the regime’s defenses, and confirmed reports that regime is redeploying troops from the already imperiled Aleppo front to Hama, indicate the regime lacks troops to hold two critical fronts at once. This is especially true in northern Syria, while the regime is performing better in and around the capital. [emphasis added]
I've blogged a number of times that both sides seem to be strategically immobile with most of their ground forces local self defense forces who are largely incapable of being massed for offensive action.
This review above about how few troops are involved in major battles indicates that this is true and that true mobile forces are scarce, even for the government.
That's why I had some hope for an earlier American training effort for rebels. If these could be mobile forces, they would leverage local forces for offensive action.
So I wasn't convinced that the Russian aerial (and logistics) intervention would be decisive. I likened it to a "sugar rush" that would wear off and leave the war still raging.
I've certainly been wrong about assessments. Four years ago I did believe Aleppo was a bridge too far for Assad to take and hold. Assad is still fighting for the city. So I've got that going for me.
But I've been very wrong about the ability of Assad's army to endure the tremendous casualties. Again and again I wondered just how much more his army could take. But still Assad's forces roll on.
Actually, I am working on a post about this error that even cites a story that prompted my still-draft post.
Basically, I think that the Syrian army essentially has collapsed already without people really noticing it. So expect that post soon.