Simpler in runtime overhead. Simpler for a developer familiar with the tools used here, but less so with others? Maybe not.

This seems to be a hobbyist project, not a major corporate effort where $100Ks were spent on tech selection.

All the complexity is handled by well known tools/libraries.

I can code a selenium script to capture a screenshot in my sleep.

Often using tools your know is the best solution.

Your free to fork this and come up with a cleaner implementation. This is probably why you need a PI Zero. Smaller micro controllers can't run a full browser.

Most of these projects are just whatever can be hacked together in a weekend.

PostScript, maybe.

Instead of generating HTML from calendar data, generate PS and have Ghostscript convert it to PNG.

I don't know PostScript, and based on the example code in the wikipedia article (https://en.wikipedia.org/wiki/PostScript#The_language), I was able to get it to draw some text in a few minutes.

When all you have is a hammer...

I would volunteer LaTeX but that's also 100s of MBs/GBs of dependencies to be fair. Perhaps an SVG rasterizer would suffice here.

Sure. But this approach sounds like a sensible base to quickly whip up all sorts of little projects.