> 1. If you customized it to speed up agendas, are agendas still slow on the latest main?
I disabled org-agenda-use-tag-inheritance but I can't provide a lot of feedback because I don't use many tag filters:
1. I disabled it in a batch script that exports my agenda, though it doesn't actually speed up the agenda (even with org-element-use-cache disabled); I guess it's because the agenda view I'm exporting doesn't do any filter (in particular, filter by tag).
2. I disabled it in my .emacs, but I guess it has no effect because I also disabled org-use-tag-inheritance, because I've never needed tag inheritance.
I temporarily enabled org-use-tag-inheritance and org-agenda-use-tag-inheritance and opened an agenda that filters by tag (it combines 4 one-tag filters), it seems to run almost as fast; 25 to 26 seconds with tag inheritance enabled, whereas with tag inheritance disabled it takes around 24 seconds. These are manual measurements which may be 1 or 2 seconds off, so you may want to measure it more precisely; they may take the same time. Anyway I don't see slowness due to tag inheritance in agenda.