Jenett's conceptualization does not suffer this shortcoming. It does seem qualitatively oriented; but beyond the first degree it also seems somewhat nebulous. Too, who makes the decision that the person involved is ready for the 2nd & 3rd degree?
Part of why it's nebulous is that it's more dependent on where people want to go with it. I've been pretty clearly on the "Want the skills to lead my own group someday sooner than later" path, which comes with a lot of "Ok, these are experiences and skills you should work on building." (group dynamics, teaching, ritual leadership, etc. etc.) A good friend and groupmate who really *doesn't* want to do that has had a harder time determining what it's going to mean for her.
As far as scheduling - really, it's the same way we schedule 1st degrees. There's some "Have they done the basic grunt work for this" (homework, assignments, contribution to the circle in appropriate ways - time, energy, etc.) But there's also "Is this the right time for them?"
Some of that is observation by the teachers and leadership. Some of it is how someone talks about their experience. Some of it comes from divination, deity work, etc. that the leadership does. Some of it's pure gut intuition (like my 2nd degree: there was no logical reason for my teachers to delay it till November: in hindsight it makes perfect sense.) Some of it's religious mystery work: has the person processed and integrated the prior set of experiences sufficient to appropriately move forward and get the full experience of the *new* set.
In the case of my 3rd, I've been on the edge of it for a bit - but one of my own requirements for myself was that I finish my graduate work first, because I didn't want to be processing the initiatory/elevation experience at the same time I was finishing grad school assignments, or the changes it will bring to my life.
2nd and 3rd are also - at least for us - very much about community involvement, experience, and commitment. Given that, the 'community' served absolutely has some bearing on how someone's doing. Certainly, existing members of the small group get a chance to give some feedback.
(They don't get to make the final decision: it's not a 'voting' process, in part because there are things that you may not notice or get until you've been part of the appropriate mystery experiences that are part of the degree rituals. But they can certainly say "I've seen her really improve her skills in X this year." or "Yes, we've had conversations that really helped me: she seems really clear on what her limits are in Y area, too, and how to work around them." or whatever.)
I also know perfectly well, for example, that my HPS and HP have gotten comments on my work on a very public event - Pagan Pride - which I do without much labelling as to my private group work. But things like "Can I work well within the broader community" make a difference when I'm going for my 3rd, and will reflect on my teachers in a broader way.
Degrees seem to me to be dangerous at best, and at worst they promote artificial divisions between people and leadership by some who aren't really qualified. Does the spiritual pilgrim really need a label to know that she can approach the gods? And leadership, it seems to me, is something that can only truly be conferred by those who would be led. Wisdom announces itself; it doesn't need a title.
For me, it seems like you're conflating a bunch of things - and saying that people who, say, want to show up for a few group rituals a year should be treated absolutely the same way as people who plan, arrange, and facilitate those same rituals.
In personal practice, degree systems don't make any sense. In terms of people in different groups, they are, at best, a very broad painted line that allows you to focus the kinds of questions someone asks to start sorting out your knowledge and background.
In a group sense, though - there are some real benefits on a purely organisational level. When we have Seekers (people curious about what we do, or considering becoming students with us), it helps to say "In our group, first degrees wear white cords: they're the best people to ask about basic stuff before ritual, like what's on the altars, or where the bathroom is: people wearing red or black cords are our upper degrees: they're more likely to be busy preparing, but they're good sources for more complicated questions, or questions about group policies."
It's also useful for our students to know that some people *have* made that greater commitment to being available - they're the people who are okay with a late night phone call, or an emergency need, or who will reliably be present at certain events to help out, wherever needed. Maybe it's just living in Minnesota, but I've found people are a lot more willing to 'be rude' and ask for help when they know there's a fairly blanket permission for some kinds of things.
I also perceive some very significant ritual, energetic, and religious mystery related changes in my own experience of a degree system. These are hard to explain, simply because they're both personal and very subjective. While I don't think these particular changes are (or should be!) required for anyone in terms of personal practice (though a couple of them have made a significant difference in my own ability to interact with my Gods), I do think they've vastly increased my ability to assist others and teach in various ways.
It wasn't just new skills: there were specific things in the three rituals I've been through (dedication, and my 1st and 2nd degrees) that opened up new energetic channels and options for me to do specific things. (At 2nd, a bunch of them were *only* group relevant: for example, like in many traditions, the ability to initiate someone into the tradition is an energetic option at 2nd degree).
If distinctions must be made, it seems to me that they should be in recognition of existing, qualitative differences, e.g., between Witch and Priestess.
Ah, but what when you're multiple of those things? (Our identifications go as follows. Dedicant: student of Wicca/witchcraft. 1st degree: initiate and witch. 2nd degree: priest/ess and witch. 3rd: technically high priest/ess and witch, though we rarely use that precise phrasing out loud.) These do rather closely mirror the layers of responsibility involved (self, assisting within a group context or with more extensive help in a limited spectrum, and being responsible large-scale/long-term for a group context, at least potentially.)