To make Anope "OperServ only" would require one hell of a massive modification to core code because OperServ's WHOLE access system depends on NickServ registrations.
And the reason you can't disable NickServ, ChanServ, etc.. and only have OperServ, is because Anope is meant as a full services package. The reason you can chose which modules you "add" to NeoStats is because the modules you add aren't core features. You can't remove the core bot from NeoStats.