Well, I've spent half a night mulling over ranks and roles, and I have come to this: Perhaps the only clear example of a consistent designation/role would be the Black ops. Standard/Soldier, while very, very common, is actually too broad to be comprehensible, and beyond that there begin problems of trying to tie in bards, engineers and just madmen. So, no designation for us indeed, I'm afraid.
The good thing, however, is that what could be done (and what I would really suggest) is the appointment of several advisers or overseers of a sort. It doesn't seem, for example, that medics (the Support, by Piecewise) would benefit from having a Master to order them around and appoint ranks as he or she sees fit, but a supervisor/guild representative which could check whether all of medics appointed for a mission have the necessary supplies and request them from the command. Sure, any medic could now do so, for example, but it may not occur to some, and others might find themselves too lazy, optimistic or whatever to actually do so. Same thing could be done with other professions; a Soldier supervisor could check if all the participants actually have the ammo, are actually armed, and perhaps request additional ammo/side weapons for the unarmed and pilots/selected few heavy weapons for missions where high resistance is anticipated, all loaned, of course. For one, Flint could have then addressed that person for a side weapon, rather than have to contend with a prototype. This way the burden of planning a mission would be distributed off the Commander's shoulders, yet simultaneously the thoroughness and completeness of preparation would be ensured.
The loaning of equipment would become more common, as would serve the hybrid system we wanted to have, with rank also having a meaning in the equipment distribution system. Oh, and battlestimms might finally see some use, if they and other consumables could be obtained more freely.
As for ranks themselves - how about these? In descending order:
0.Steve - Well, the one and only. Until we replace him, of course
1.Generals - People who have broad authority in all matters of the ARM. They are tasked with being as wide-planning as possible, as their actions and decisions have the most deep and broad consequences. Upon the choices of these people the whole future of the ARM depends.
Note that I consider it possible for further Generals to be appointed, however, the bar is intentionally set as high as possible to filter the more focused-minded people.
Benchmark: Miyamoto.
2.Commanders - People who are tasked with coordinating whole missions or leading specific projects. They share the Generals' right of ultimate authority, albeit in their specific field, and, in times of desperation and turmoil, they are to be considered Masters under Steve, answerable to him only.
Benchmark: Simus.
3.Lieutenants - The lesser leaders, tasked with commanding a squad and assisting Mission Commanders with planning, preparing and executing missions.
Note: Depending on how you go, advisers/supervisors could be either this rank (if they are mission-assigned) or the above rank (if they are tasked with helping prepare all of the missions; probably latter). Otherwise, it could be that squad leaders Lieutenants could also have say in mission preparation and possibly request materiel to cover the needs of their particular squad (especially if it is tasked with a different objective and role than the rest of the mission).
Benchmark: Lars (and many others).
4.Adepts - The highest ranking non-leader characters, they are the most grizzled, skilled and competent among the non-leaders. Still, should all of the mission command be removed, it is them who will have to guide the surviving characters towards the mission goals or simply the extraction site.
Note: I don't quite like the idea of forcing non-leaderly people to take command, but naturally the most accomplished veterans would have the authority and competence needed to salvage the mission.
Benchmark: Mesk (at M15)? Mostly the way how he reluctantly took over command realising he was the only remaining veteran out there. I might be mistaken, though. Otherwise pretty much anyone to be considered a (at least moderately) competent veteran.
5.Regulars - The bulk of the characters, the people who have been to an irradiated hellhole called mission area, and come back. They may or may not be competent or particularly skilled, but they can and hopefully will do fine. In two words, ordinary and dependable.
Note: Ordinary in context of the former 'Corps.
6.Novices - Not quite a rank per se, but more of a lack of any particular rank. Mostly because they are just fresh out of the stasis pods.
7.Hazards - People who prefer to have fun above all, or have a similar reason not to care too much about reaching mission goals safely and carefully. Sometimes described as incompetent, they might just be careless, or slightly foolish, or even deliberately unfortunate. Whatever the reason, they are who the leaders want to watch more closely and, at times, prohibit from acquiring or using some of the more dangerous equipment. Might actually be competent or at least not actively incompetent at times.
Benchmark: Stacy (Mission 15)
8.Immediate Hazards - These you should be wary of, and probably even fear. They have proven their danger to foes and friends alike, and are set in their ways. Friends of casual overshoots, they may not be incompetent as is, but are still very dangerous by every time of their employment. Require constant monitoring and potentially safety measures.
Benchmark: Xan-1 (Mission 15)
To keep things impartial, yet definitive, I suggest that moving down within the ladder is a public decision, say, by a minimum of three other characters (meaning the rest of the smallest team minus one person), and moving up is decided by the higher-ranking officers. That way Hazards and Immediate Hazards could be appointed by their peers, yet it would be up to Commanders and above to decide when people have improved to be considered a rank higher.
Finally, the ranks system so far (or, at least where it concerns the non-leaders) should be considered as guidelines rather than set rules as far as giving out equipment is considered. I.e., mostly as it is, only giving form to unspoken agreements and traditions of the ARM and the former HMRC.