Some of you make more or less implicit assumptions. I let you think about these assumptions, below are some of them.
A player strength (or skill level or whatever you call it) can be reduced to just a number.
Thus, if player A is stronger than B, and B stronger than C, then A is stronger than C.
This number does not fluctuate (time, computer, internet, game settings such as civs, map, starting resources, positons, etc).
You can always easily predict the outcome of a match just based on these numbers.
The strength of a team is just the sum of the individual strengths. A variation of this assumption is: the strength of a team is just the sum of the four best individual numbers.
Players and observers won't have fun with the current teams.
Any player would accept to team up with any other player.