In an ideal world, the HTML rendering infrastructure would have been built atop a lower level representation that was also accessible to JavaScript and allowed for the construction of one's own rendering loop and pixel by pixel manipulation. This doesn't exist, but you can kind of imagine what it would look like if you imagine a world were the HTML rendering architecture was just a library that ran atop webGL.

But that isn't the world that is exposed to web developers, so a lot of complexity is necessary to take a declarative rendering language and trick it into giving developers the kind of control they need to address issues like the naive solution for altering the declarative tree and triggering a repaint not necessarily cohering with what users consider "good looking."