I don’t disagree with your statements.
Even so, I think everything is tending to degrade the long term importance of Assad. I think without the Sunni dominated “Syrian opposition” gaining anything, the various forces that are not Assad’s that are being backed by Iran and Russia will in time (????) be able to officially displace Assad, as a figurehead they will no longer need - they will be stronger than Assad, they will be Shia dominant and Assad will not have Sunni Syrians to call on for help. The beneficiaries of those forces reaching that state will be Iran and Russia. They will jointly arrange a replacement for Assad. He will go into exile.
Syria is effectively partitioned now. What is left to resolve is Assad’s hold on the northern enclaves under attack by Turkey. They may get partitioned away to Turkey and its militias.
...........
That would be a critical loss to Assad’s push to hold onto NE Syrian territories along the Turkish border. Those are currently patrolled by Russia and are quiet for now.
...............
Turkey has made a very risky move into the Libyan fight and it is bogging them down. Turkey also is staying away from the Russian-manned air defenses in N Syria.
...............
If the Turkish fight remains a stalemate and Assad continues to hold onto Alawite and Christian and Russian support, he can hang on, whether Iran support remains.
................
Russia is desperate for their Syrian base at Tartus and is gradually moving more assets into the Med. I think that settling the ISIS fight in W Iraq will be the next tipping point.