files in env.d get exported to the environment of all processes, even ones unrelated to distcc. distcc-config writes out a bunch of variables there, even the default values. this just adds overhead/noise. please make distcc-config smarter so it only writes out settings when they are different from the default.
Additionally, configuration in /etc/env.d/02distcc with distcc-config seems to override configuration in /etc/systemd/system/distccd.service.d/00gentoo.conf as proposed to use in the wiki page of distcc.