That description just sends us back to square one though... by definition a team is a bunch of different people coming together for a common goal. Just saying "A bunch of people allying" Doesn't actually describe anything about the group. The grunt plan has a base in the mainstream games (The actual grunts from the actual teams) So it gives us a face and appearance, but its not so strict that we can't be creative with it. There obviously wasn't an inter-team grunt alliance, so we can pioneer our own ideas in that respect.

Essentially we're the Pokemon version of Spartacus' army. All the rejects and front-line fighters no one really cared for coming together to show we're not as insignificant as everyone once thought.

Or if you prefer, it's like in Strike/Union movies where the low working class rebel and show that the big money makers wouldn't be able to do anything without them.