(Disclaimer: I'm a Vega-Altair maintainer)

Thanks for the feedback and for the kind words! All of these drawbacks are fair, just a couple of comments.

There is an experimental package called altair_tiles that makes is possible to add OSM-style maptile backgrounds to Altair charts. See https://github.com/altair-viz/altair_tiles. This is mostly for static charts at the moment, as it doesn't integrate well with pan/zoom yet.

As you mentioned, VegaFusion is able to remove unused columns in most cases. (And if it doesn't for a particular case, please open an issue!).