> What are its advantages? > There is only one rendering engine, cutting down complexity.

Actually there are 2 rendering, the server sending HTML and the browser drawing it on your screen.

So why not push the logic and send a jpg image of the rendered content itself. Lol

The whole concept of decoupling the frontend and the backend is that they can be agnostic of each other, they need to align but it is not the same skills/concerns.

Serve rendered html like in 2000 and you have recreated a smart way to do what industry spent decades running away from.