Not sure when or how the improvements to rendering on the maps took place, but the end results, especially for small text sizes, are awesome. Thanks to those who made that happen. It is a vast improvement in useability.
Topic on Template talk:Graph:Street map with marks
So it turns out that the improvement is the result of WMF shutting down graphoid (https://phabricator.wikimedia.org/tag/graphoid/) which used to render the maps and just pass on a fairly low-res image. This happened during early 2021 I think, but it is not clear if anyone looked at the implication for the mapping stuff. The improvement in clarity of the maps is massive, but at what download and resource cost?
With graphoid there was no overhead to adding as many markers, details, items etc as an editor wanted. Is it now rendered from scratch every time? and what is the implication for mobile data users in particular? If anyone can offer an observation or reassurance on these points (maybe 'varnish' can keep it all in bounds?). I note some references to 'maps 2.0' https://phabricator.wikimedia.org/T280767, being worked on, so we may have to see what is coming next.