at least adding three minor indexes as suggested by https://github.com/ankane/dexter seems to have lessened the read stampede

CREATE INDEX CONCURRENTLY ON "public"."nostr_events" ("created_at");

CREATE INDEX CONCURRENTLY ON "public"."nostr_events" ("pubkey", "created_at");

CREATE INDEX CONCURRENTLY ON "public"."nostr_tags" ("event_id");

although public.nostr_events (kind, content) isn't possible to add because that has txt longer than the 8191 size limit