I’m on MacOS 15.4.1 (Sequoia) and can feed back, that Safari shows the markers with increasing sizes while zooming in, just like your screenshot.
In Firefox (137.0.2), markers don’t grow beyond early on and are then shown as constant sizes when zooming in, which makes them hard to read:
P.S.: playing with it a little longer I see, that also in Safari markers don’t grow infinitely (which is good, imo). But the “clamping” sets in much later when very good readability is given.