Later Hacks And Mods
It is true that in the further development of Apocalypse World and games deriving directly from it, the Aid move has been weighed in the balance and found wanting.
In the second edition of Apocalypse World the Aid or Interfere move has been expanded to a straightforward +1/-1 on 7-9 and a +2/-2 on a 10+. Just saying that on a 7-9 you expose yourself - well, it makes sense on the Interfere part of that action, but during normal gameplay, if you Aid someone, it's quite likely that you're in the soup with them already.
In other places, people have turned the Aid move into "as long as you have a bond, whoever you're aiding rolls 3d6 drop lowest instead of 2d6", but those games tend to have fewer bond slots than Dungeon World, so I find a good compromise is that you have to mark an unmarked Bond with who you're aiding, and you erase your marks at end of session or when you Make Camp.
But even without those modifications to it, with the move as written, the odds are-
Never Tell Me The Odds!
Shut up, guy who shot first.
Anyway, even without those, Aid isn't that long odds. If you have even one bond with the person you're trying to aid, there's a better than 2 in 3 shot you'll be handing them another +1. Two bonds means it happens 5 times in 6.
And a +1 is a pretty big deal in Dungeon World. It's going to halve your chances of failing a roll, or double your chances of getting a clean 10+ hit, or it doesn't do either (+0 or +1 base modifier) but it comes pretty close to doing both.
Limit One Per Customer
Though you are right in that the more people who are lined up to aid somebody, the more likely things are to gang aft agley, both because of the odds and because it's likely that successive people haven't written as many bonds. So in places where everybody's trying to make something positive happen, ask that the best person for the job roll, and their best buddy help them out. In places where some great calamity will drag everybody down, ask that the worst person for the job roll, but their best buddy can still help them out.
And remember, a 6- doesn't mean that a PC must necessarily have failed at what they were trying to do. It means that as a GM you get to do whatever you want, and that can include passing the aid bonus to the PC who would act next. It's just that it can also include passing the aid bonus because a nice young man in red robes pointed the way, oh look, he's calling all his friends, they seem so eager to come in here and help, and they're all bringing torches to help you look in the dark corners!
It would never include sarcasm. Perish the thought.
For Everything Else, There's Homebrew
Of course, there are the occasional big dramatic scenes where everything comes together, where everyone's got a part to play in building some machine or searching the treasure room or scouring the Infinity Fair for the last phoenix feather in existence. And, I mean, when you thought about a divine avatar of judgement and Defy Danger wasn't adequate for the task at hand, you wrote a custom move. When you thought about an ancient labyrinth and Discern Realities wasn't adequate for the task at hand, you wrote a custom move.
You did, right?
Well, if you think about something so big that Aid or Interfere isn't adequate for the task at hand, you can write a custom move. Something like:
When you all spread out and search the Infinity Fair, everyone pick a stat:
- +WIS to quickly scan the stalls and pick up or rule out traces of a phoenix feather
- +CHA to ask after one without alerting attention to yourself
- +bond with someone who's rolling one of those other two (limit one per)
Roll 3d6, keep 2, and add to your total. On a 6-, muahaha. On a 7-9 you make good progress. On a 10+ I'll also tell you something interesting that you find for sale.
But that's not what you're really after here, is it? You choose which dice to keep for yourself and which to contribute to the party.
If your contributed dice average to at least 5, I'll name and describe some people who might have a phoenix feather up for offer and what they trade in, and you can tell me who has it.
If they average 4 or more, but less than 5, I'll tell you who has it.
If they average less than 4, I'll tell you who had it, and you can probably get them to tell you who bought it from them yesterday.