Well without getting into the debate over the level of Assad’s responsibility for what has happened, I’d say that even in your generous evaluation he still comes off looking worse than the SDF to the average Westerner.
As for Kurdish ambitions, it’s true they have over-stepped their boundaries in certain areas, but at the same time they are surrounded by hostile states and still without a state of their own. So what you and
@syrian_scholes may see as land-grabs in Kirkuk or Deir Ezzor, they probably feel is, at a minimum, a guarantee of being taken seriously at any future negotiation table. In any case however, whatever irredentist ambitions they have had have been ruthlessly defeated time and again.
I’d also add that while you guys see the Syrian and Iraqi states as sacrosanct (correct me if I’m wrong, just the impression I’ve picked up here), they lack legitimacy in many Western eyes. Ironically this is primarily because we’ve had almost a century of Arab nationalists telling us that the borders were imposed by Western imperialists and that they’re therefore illegitimate and need to be corrected. So when the Kurds argue along the same lines they tend to have a ready audience in the West (although those same Arab nationalists generally tell them to get fecked).