I recently took part in three team missions and racked up a whopping 8 levels literally overnight, (from 56 to 64). GREAT, but...
I got 6 tokens out of the deal.
Since there are SO many more mobs in team missions, taking team missions is a good way to NOT keep on top of your token board.
Here's my suggestion. Instead of each mob's death being worth a percentage chance of getting a token equal to 100/(the total number of mobs), make each mob worth 5%. A flat 5%. Then, make sure you can have 200%, 300%, even 5000% or more, chance of getting "a" token. For each even 100%, give the player a token on completion. For the remaining amount, roll as the system currently does. So if I or my team kills 50 mobs, then that would result in a 250% chance of getting a token. Since each token is worth 3 to me right now, that's 6 tokens worth guaranteed upon completion, and 50% chance of another 3 tokens worth.
I'd take it one step further to promote outdoor hunting. Those mobs around the boss mob. Make each of them add some percentage chance of getting a token as well, once the boss mob has been killed...by anybody, provided you're still in the area and on-line when it happens.
This way, missions with more mobs are worth more tokens, while there is a distinct possibility of not getting any token if you took an "easy", low mob-count mission.
Making the mobs worth a flat percentage should be easy. I'm not sure how much effort would be involved in making percentages over 100 possible, or implementing multiple token rewards.
An aside. If you implement this system, you might want to rethink the multiple token value of mission tokens that come with title-levels.
Also, if you do this, each player should have "his" token chances tracked separately, so a person actually needs to be around when a mob falls to claim the percentage, instead of just part of the team but outside when it happens.