Most 'fullstack' positions don't have nearly the complexity where worrying about concurrency etc. is actually that relevant. The idea that most frontend devs have any knowledge about optimising for browser paint performance beyond using the correct CSS or framework is funny ;-)
I know, we have seen insane developer inflation the last 10 years.
The bar is generally just a lot lower now across the board. We have people with the title "Senior Engineer" that still regularly need mentorship and peer-programming sessions.
The title I have now (Principal Engineer) I feel like I don't deserve, it was reserved for folks I looked up to when I was starting and I don't think I have reached their level. Yet at the same time it's essentially necessary to distinguish myself from what is now considered "Senior".
I have a separate rant for the lack of proper juniors and lack of structured mentoring etc but that is for another day.
