This is, in my mind, orthogonal to the systemd question. I used to be able to say Linux was clean, logical, well put-together, and organized. I can’t really say this anymore. Users and groups are not really determinitive for permissions, now that we have things like polkit running around. (Yes, by the way, I am a member of plugdev.) Error messages are unhelpful (WHY was I not authorized?) and logs are nowhere to be found. Traditionally, one could twiddle who could mount devices via /etc/fstab lines and perhaps some sudo rules. Granted, you had to know where to look, but when you did, it was simple; only two pieces to fit together. I’ve even spent time figuring out where to look and STILL have no idea what to do.
systemd may help with some of this, and may hurt with some of it; but I see the problem more of an attitude of desktop environments to add features fast without really thinking of the implications. There is something to be said for slower progress if the result is higher quality.