Most Efficient Web Development Build Process

For most of my career I've worked with a small team where backend and front-end development tasks where split between specialists. We had a waterfall like process where designs were supplied to the front-end developer (me) and flat (no CMS/API) version of the site build was created. After initial approval of the flat, the backend developer would create templates of the HTML files and integrated them into a CMS (e.g. WordPress, Drupal, ExpressionEngine). Any further front-end development would be carried out on the now created backend templates.

Is the above process the most efficient? If say, you're developers were full stack developers would it be more efficient to go straight into the backend setting up the templates and CMS and build up the site from there to match supplied designs?

For a bit more context, the typical sites are small projects and microsites where the lifespan may only be a few months to a couple years. I've just joined a small agency where I have the opportunity to push to train as a full stack developer and learn backend, or I could suggest and push for developers to specialize in front-end and backend roles and implement a build process similar to my previous agency.

Any tips or advice? I'm trying to assemble a list of pros/cons for each process. Thanks!!!