Syria is 74% Sunni Muslim.
Assad is an Alewite which is a Shia sect of Islam.
The Alewites and Shias (Assad’s power base) are outnumbered 4 to 1.
Trust that Assad populated the the officer corp (certainly the pilots) with Alewites and Shia. Assad would NOT want a disgruntal Sunni pilot dropping a bomb on his palace or defecting with a fighter jet.
Given the demographics, we can assume Assad’s infantry (the grunts) was majority Sunni. They have long since deserted or otherwise have no interest dying for Assad.
You CAN NOT take back and hold territory with air strikes, tanks and/or artillery strikes => UNLESS you have infantry to occupy the territory.
Russian air strike are not a game changer. There is a sniper rifle sticking out of every rat hole in Syria, Russian air strikes won’t change that.
That's what the Iranians and Kurds are for.