Wagner Mercenaries and Hezbollah provided the brutality in Syria.
Putin had to use his Mercenaries in Ukraine. Iran decided to attack Israel with Hezbollah. All of a sudden, Assad is exposed.
Also, I wouldn't be surprised if most of the pilots manning the helicopters and planes were Russian. But now they're all in Ukraine. So Assad can no longer have air support to take out the enemy before they attack.
Years ago, I saw a video that followed a Syrian Airforce pilot through a mission from start in the briefing to finish. My guess is he was in his mid to late fifties. He looked to be substantially overweight. He had the all upfront belly I would call a beer belly. The plane was either a MIG 15 or 17. The video pointed out it was OLD. The ordinance was something like an oil drum packed with explosives but with wooden fins bolted on. The pilot had some ridiculous number of flight hours. I don’t recall the number, but the narrator made mention it was a LOT of hours. The plane was already ten years late to the bone pile and I’m sure it was probably one of their better ones as you wouldn’t put a super experienced pilot in one of your less usable planes. My guess; there effectively wasn’t a Syrian air force as it aged out long ago.