I never viewed full stack as knowing all the technologies. Rather, I view it as the ability to solve the problem end-to-end. Often, knowing a few generalizable recipes is sufficient to be effective in this regard.
That's how I view it as well. There are some parts of the stack where I am more proficient than others, but I know I'm able to onboard pretty quickly to start solving problems regardless of whether it's frontend, backend, infra, whatever. I guess when I think of full stack, in practice I think of someone whom the linked article describes as T-Shaped: probably especially proficient in one thing, but able to rotate and be useful wherever needed.
I completely agree. I don't expect everyone on the team to be like this but having seniors that are is very important. This subdivision of tasks does result in an "over the fence problem" and people need to work both sides (all sides might be a bit much but having people work at least partially beyond their title is something which is overlooked)