It doesn't really defeat the purpose. It just shows how much fuss about avoiding JS is a sign of insisting on ideological purity rather than accomplishing any particular goal.

What exactly is the difference between generating HTML using the browser's XLST 1.0 runtime and SaxonJS's XLST 3.0 runtime? Before you say the goal is to not have to deal with JS, then you've already accomplished that goal. You don't need to touch NPM, webpack, React, JSX, etc.

Blocking first party JS is lunacy by the way.