That said - to the question about unicorns: You're always expendable. Same as any job - same politics - same nonsense. No matter how important they make you think you are to a products success - they'll fire you regardless. It's amazing how fake management will be about urgency. "This is the most critical business function! We must have people working on it!11!!1!1!" Fires key employee because they didn't like them - "critical business function" gets shoved into the backlog to never be seen again. People are fake and think they need to show urgency to get the most value out of their employees.
Never worked for a unicorn, but everything from big corp to startup to government. "Urgent" provokes no reaction from me anymore because of this.
On the other hand, artificial deadlines that are invented by your company's management are usually not urgent.
,"Critically Important", etc. is the most recent whatever caught the attention of a typical S/E/VP with the attention span of a ferret long enough for him/her to be able to utter it in the words. If you're able to highly visibly jump and demonstrate activity during exact that moment - a great talent leading to advancements/promotions - there is no point to react as the next new "critical" directive/change of course/etc. is coming very soon. Of course if your manager is one of those aspiring "talented jumpers", he/she will try to make you jump with him/her - it is a real PITA to have such a manager who instead of filtering and protecting the team from would amplify all that stuff flowing down.
I call this "artificial panic". That term came to mind when I joined a FMCG around Y2K, and on my first weeks I noticed people were running around stressed, like headless chicken. When I asked "what's on fire" and the answer was "nothing".
https://dilbert.com/strip/2012-07-15
The "Minimalists" say on their podcast that "most emergencies, aren't". When I see panic setting camp in a company's mentality, I make myself scarce for a while until things calm down. If I see that the artificial state of panic is a perpetual feeding machine, I try to dance around it. I've read my share of Dilbert to know to avoid these toxic environments.
Sometimes you need to be a Wally to survive.
Ideally in a company there would be one single order backlog, showing the relative value of each project to everyone. However getting such an ordering would involve huge co-ordination across vastly differing internal companies / cultures and would drag up every buried political hand grenade of the company's lifetime.
So instead you do what someone shouts loudly about. If the shouter is right more than 50/50 they are doing pretty well.
The whole point of "Agile" was supposed to break down these divisions. Management is "generally charged" with getting the greatest productivity they can out of their resources. How that productivity is measured may be by "the priorities as set by Product", but that doesn't take into account ROI, sunk costs, COGS, Cap/Opex etc etc.