I had to manually strip here: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=205060 even though 'make stage' command recommended to use INSTALL_TARGET=install-strip.
Another example is devel/py-cffi
You misread the message, it is: "consider trying INSTALL_TARGET=install-strip or using ${STRIP_CMD}" INSTALL_TARGET=install-strip is usually for autoconf based ports. If it doesn't work you can still run ${STRIP_CMD} in post-install.
I think this should be made into USE_PYTHON+=strip I will submit a patch