[Boldened15]

It really depends on the product (or feature) how much of that expertise is necessary. You need some domain experts for sure who really know the ins and outs of the specific backend and frontend technologies to architect the overall app and build system, and do the hardcore stuff like optimization that you mention.

But fullstack engineering is just much more individually productive, if you're updating a settings page why involve multiple engineers and coordinate a handoff, when one engineer can just add the API calls on the backend and add the new toggles to the frontend in a single day? Most software doesn't need to be beautifully polished and completely excellent.

Anyway I personally just find it fun, I get to breathe life to a vision end-to-end and tackle a wide variety of problems, and I can deliver quickly. Even if I'll never be (and don't desire to be) a super expert in one technology.