So as long as the rogue is contributing to the fight with the elemental in some fashion, you're OK with that? (I'm keying off your use of 'binary' here.)
If so, what degree of reduced effectiveness is acceptable and what not? For example, the rogue could have (instead of stepping out for a smoke) tumbled into a flanking position and fought defensively, to give the fighter a flanking bonus and allowing him to inflict more damage. He's not hurting the monster, but he's not useless either. Does the rogue need to be doing 80% of his normal damage at minimum before he's considered to be contributing?
That's a very good question, and I think its very hard to judge within the context of D&D's general rules...and not all answers equally satisfy all players. However, this is where I think abstract player-level mechanics and resources shine the best. If you can make the character actions and effects sufficiently flexible narratively and potent mechanically, then you don't necessarily have to worry about trying to balance different flavors of fiddly bits like 3 HP and 5 ft of forced movement and imposing a condition. In Fate or Cortex+, for example, this balance issue doesn't come up, even with strongly-typed characters. A wide variety of skills/traits/abilities can be leveraged in a wide variety of circumstances, limited more by the players' creativity rather than the rules governing the skills/traits/abilities themselves.
However, that doesn't seem to be the trajectory that D&D has generally taken.* Instead, D&D has increasingly leaned towards defining characters as collections of tiny scripts (some with more flexibility than others). I'm not just talking about 4e, either, although that incarnation arguably took the principle the farthest. In the early editions, its most evident in the spellcasters. However, by at least 2e, other character types were getting in on the act as well, either through proficiencies or kits or other tweaks available in various forms. 3e got crazy with not only scripts, but script-modifiers flying all over the place (although for many classes the tiny scripts were disguised fairly well). 4e just came out of the closet and explicitly gave them to everybody. But!...
I think this trend is problematic because it also subtly emphasized a divergence between combat (where most of the little scripts apply) and non-combat (which, in spite of Skill Challenges, became less regulated as time went on.) The only instances of anything remotely similar to an AEDU system for the "interaction pillar",
might be in Dungeon World or Old-School Hack (but I think that's a stretch for other reasons). Similarly, while the
details of exploration might be more defined (i.e. X DC to jump Y ft.) exploration overall became less regimented (loss of "turns" vs. "rounds") as a mode of play. This makes for problems when different character classes specialize in different arenas, problems which are often called "balance" issues.
I also think the scripting trend makes balance (of the sort noted above) tougher from a design point of view. In older editions; when 5ft steps, feints, swings, and the like are swept under the rug of minute-long combat rounds; HP are abstract enough that some of those things must be incorporated into them (even if we fail to note it, narratively). In such a system, its fairly easy to say that class A does X dpr fairly regularly, but class B does 3X, but only about .33 of the time. Tossing in fiddly bits like the flanking bonus mentioned above both clouds which character gets "credit" for damage dealt, and exacerbate narrative issues with HP in general. I suspect that one of the reasons 4e has such a tight or strict feel to its tactical combat and related rules is so that the relative values of such bits remain reliable.
DISCLAIMER: The above is not intended as, nor should be construed as, an indictment on D&D or any of its editions or incarnations. Nor is the Fate/Cortex+ way of doing things perfect for all players and purposes. This is merely an observation and related suspicion on my part.
*Which may be for good or ill, and may be for a variety of reasons; business, design, or otherwise. I'm also not yet confident of how I would assess 5e in this regard.
