If being down about your job causes symptoms of depression that last more than 2 weeks, then it's the same thing. Psychiatrists diagnose based on symptoms. Worse, its usually what you say your symptoms are, with words and talking. They don't scan your brain. I've been seeing psychiatrists for almost 30 years. The good ones take plenty of interest in your situation, lifestyle, and other non-chemical non-medical factors. Psychiatrists don't distinguish between so-called 'situational' and 'clinical' depressions. Laypeople do that. If you get diagnosed by a clinician, that is the part that makes it clinical - it isn't a different kind of condition.

That is an incredibly dismissive and reductive argument to make. "Feeling sad about your job" isn't limited to burnt out software engineers with a safety net. It can also apply to, for example, someone stuck in a shitty, low paying job with few, if any, prospects for better employment. The lack of a path to a decent future can, in itself, be incredibly demoralizing, even if your present circumstances might be decent. After all, what's the point in continuing if I can see that it's all downhill from here?

That isn't major depressive disorder either. Even if those people think their life sucks, they're capable of, say, getting out of bed every day and don't regularly attempt suicide.

Russian serfs might've revolted when they got the chance, but they were more or less psychologically normal until then. Their society adapts to not kill them all. (Or they all become alcoholics or something.)

Bad jobs can cause suicide

Suicide is usually due to distress than clinical depression. This is why suicide hotlines work at all.