Off the top of head it would be balance based on combat parity with the encounter as the focus of balance (instead of balancing things over the adventure or campaign). Along with other features like gamist conisderations taking precedence (making sure characters canheal fast andget back in the game, that sort of thing).
OK. I like your breakdown of balance at the encounter level vs. balance over the adventure vs. balance over the campaign.
Now I'm thinking, what about balance at the round level? Everyone is guaranteed to be exactly as equally effective each and every round.
That would be unfun though, because if things are absolutely balanced all the way down the line, there's no challenge. There's no space between good and poor play.
Absolute balance is antithetical to good gameplay. Tipping the balance in your favor is where the fun is. We don't want more or less balance, we want more or less frequent opportunities to tip the balance in our favor.
We're considering different lengths of time the game might force you to go between these opportunities. This is equal to the space between the time unit below the unit at which the game is said to be balanced.
So, a game balanced at the encounter level means you have opportunities to tip the balance in your favor each round.
A game balanced at the adventure level means you have opportunities to tip the balance in your favor each encounter.
A game balanced at the campaign level means you might have to go whole adventures without an opportunity to tip the balance in your favor.
Just a different way of looking at the issue, perhaps.