To the contrary, I feel the distinction to be very arbitrary and especially in the context of web applications so muddy it’s almost useless. Who is responsible for websockets? CSP? JavaScript chunk caching? Web worker edge deployment? File uploads? HTTP/2 stream usage?

The web as a platform shouldn’t be constrained by two arbitrary, isolated boxes, because that’s not how it works. A software developer writing code necessarily has to get involved with stuff running on client and server devices and everything in between them out of sheer necessity, if they even want to understand how modern technology works in this space.