The skill challenge system was designed and intended to include the entire party.
Skill Challenges get run different ways by different DMs, but many require everyone to roll
I don't want to derail too much, but this reminds me of why I think the skill challenge guidelines are so poorly written.
In combat, the reason that every player rolls is (i) his/her PC is under attack, and (ii) his/her PC has something to offer to improve the situation, both for him-/herself, and for the party as a whole.
A GM who wants everyone to take part in a skill challenge should, in my view, be framing the situation so that (i) every PC has a reason to do something - is under some sort of pressure - and (ii) every PC has something viable to do to relieve that pressure, and the pressure on the party in general. (Even if that viable thing is only stalling until another, defter PC can extricate him/her from the situation - in one social skill challenge I ran, which took place at a dinner party, the smooth-tongued sorcerer said to the dwarf fighter, who was doing a lousy job of trying to keep secrets, "Derrik, time to take a piss!" - thereby defusing the situation, at least temporarily.)
Fighters have crap for social skills. The one social skill they have in class - Intimidate - is used in sample social SCs as an example of an automatic failure. Fighters are still pretty hosed.
A complexity 5 skill challenge is only likely to involve 20 rolls or so (up to 14 primary checks, plus whatever secondaries are used). In the challenge I mentioned above, the fighter only made three checks, I think - a failed social check early on, the Intimidate check that ended the challenge (he goaded an oppposed NPC into attacking rather than just leaving the dinner party), and an Athletics check - made while agreeing with the host's remark that "I am a man of action, not words".
I'm not saying that fighters couldn't benefit from a better range of skills, but even with a very short list it should still be possible to play a meaningful role, provided (i) that the GM frames scenes with the party's capabilties in mind, and (ii) that players are prepared to engage the fiction rather than try and run mechanical roughshod over it.
Everyone needs to generate successes (or at least non-failures), so everyone did what was most likely to succeed. The fighter, in particular, was forced into an extremely awkward position due to the fact that he needed to generate a success, and his scores with skills that would have been traditionally used in such an encounter were rather underwhelming. So, he improvised with the only thing that might work.
I understand this. I just don't think it sounds like very good scene-framing or adjudication. I mean, why (in the fiction) did it matter that the fighter do something? What bad thing was going to happen if he didn't?
I've got nothing against running skill challenges that make everyone take part, but I think the fiction has to make sense of this. Otherwise how do the players know what the sensible options are? Without embedding the challenge in the fiction, I don't see how you avoid the notorious "skill challenges are just a dice-rolling exercise".
To put it another way - I don't quite see how the backflip episode fits in with what the DMG has to say about skill challenges:
You describe the environment, listen to the players’ responses, let them make their skill checks, and narrate the results...
When a player’s turn comes up in a skill challenge, let that player’s character use any skill the player wants. As long as the player or you can come up with a way to let this secondary skill play a part in the challenge, go for it…
However, it’s particularly important to make sure these checks are grounded in actions that make sense in the adventure and the situation… you should ask what exactly the character might be doing … Don’t say no too often, but don’t say yes if it doesn’t make sense in the context of the challenge.
It doesn't sound to me like the performing of the backflips was "grounded in actions that make sense in the adventure and the situation", and that in turn sounds like it may have been because the GM had not "described the environment and narrated the results of previous skill chekcs".
Conversely, if I'm wrong about that, and the king had just said to the fighter "Why should I take you seriously as someone meriting aid?" and the fighter responds by performing some feat of physical prowess - thereby demonstrating that only he can do the tremendous thing that has to be done - then why
shouldn't that be viable? If that's what happens, then it sounds like the player of the fighter chose to do a silly feat of prowess - backflips - rather than something more fitting like (say) crushing a goblet in his fist.
Also, a 'they also serve who merely stand and wait' clause for SCs might be called for - especially if they go through with balancing across pillars, so you have characters who must suck at exploration or interaction or both to be good at combat - SCs in such a system would be horrid failures if the dead weight wasn't allowed to, well, wait.
Personally, I would prefer that they pay more attention to advising GMs how to set up and adjudicate situations that don't require either waiting or absurdity to work. But given their inability to write effective guidelines for skill challenges to date, despite three attempts (DMG, DMG2, Essentials) and despite the existence of plenty of good models (HeroWars/Quest, Maelstrom Storytelling, and to a lesser extent Burning Wheel), I think they will probably go for the "wait" option instead.