Deep knowledge of what? The way different browsers render things?
All of the Web dev I've been involved in is pretty straight forward stuff to manage records in a database or make it easier to interact with the records on a browser.
The only thing remotely complex was 3d rendering. Perhaps I have a narrow view of what is considered web dev now.
"Webdev" is not fundamentally any different from any other kind of development that involves a client and server component. It just happens to be served in a web browser. You need the same underlying knowledge as for other (common) types of software development.
All of the Web dev I've been involved in is pretty straight forward stuff to manage records in a database or make it easier to interact with the records on a browser.
The only thing remotely complex was 3d rendering. Perhaps I have a narrow view of what is considered web dev now.