I think you're missing the point.
A full stack developer is not an expert in everything, he/she is good enough to get most of the tasks done. There is still room for experts and specialists, but not every task requires one.
For example, a full stack developer can probably build a working prototype, but to build a production ready product might require some experts in different fields.
I consider myself a full-stack developer/architect, my focus is mostly on building solid infrastructure and backends, but I do write frontend code as well, doesn't mean I'm an expert at building UIs, but I do a good enough job for it to be usable and production ready.
I am a Full Stack & DevOps Engineer. Jack of All trades, master of none, certainly better than master of one - At least as far as nascent startups are considered. I Architect, design and implement front-end, backend and mobile applications. I also Deploy and manage the servers. Just enough stuff to get the product of the ground and get it running on production (an MVP). After that, people hire specialists as required to build upon it.
Hiring many specialist is a luxury that a nascent startups with limited capital cannot afford. Full Stack best suits those situations. But as the company grows, it should opt for specialists.