dev-libs/mongo-c-driver and dev-libs/libbson are the only packages pulling in sphinx without having a doc useflag.
if (ENABLE_MAN_PAGES STREQUAL ON OR ENABLE_HTML_DOCS STREQUAL ON)
find_package (Sphinx REQUIRED)
So USE=-doc should disable ENABLE_MAN_PAGES and ENABLE_HTML_DOCS and compile without sphinx.
and this is worse than i thought:
dev-libs/mongo-c-driver/mongo-c-driver-1.17.0.ebuild: line 6: please migrate from 'cmake-utils' to 'cmake'
Created attachment 656212 [details, diff]
Created attachment 656214 [details, diff]
Further clean up can still be made however this allowed me to compile the packages and clean up sphinx from my system, saving 18! packages.
USE=pic could be added.
Created attachment 656324 [details, diff]
Created attachment 656326 [details, diff]