The presence of the Load 300 button does not mean that I always use it)) This is a crutch button to load enough changesets for filtering. If you don’t take a city with active cartographers, then there will be a bunch of large bboxes in /history that I can filter out. (or hello to the OZON map team, which floods changesets)
The problem is different:
- With the script, more changeset are placed in the sidebar in the visible area
- Now on the map you see in the worst case 4 similar bbox colors:
- changesets above
- visible changesets
- changesets below
- changeset under hover
If earlier I could hardly find the edit under the hover because of the bad color, now there is even more color noise among which I need to find the active changeset.
I would take the risk to try not to show any non-visible (in sidebar) changesets at all 
Also, sometimes the hover fails and the bbox ends up not on top of other bboxes:
Alternatively, I want to play around with different bbox colors for different users, as done in Easy Changeset Viewer(ver 2025/03/29) and a hover for the usernames that highlights all their changesets
But I have to admit that this only works because of map discoloration
But if you dig deeper, only JOSM and iD’s built-in ability to split changeset into several small ones can put an end to interfering bboxes. Or an API that provides meta information about clusters of objects in changeset.