Camerupt is a good example of this; we would be able to take on zapdos, scizor, heatran and celebi to an extent given enough of a boost in the right areas. In this way he would be a decentralizing force.
As the_artic_one said, if every concept was in the interest of decentralizing, that would be the only viable concept. I, like Magmortified, fail to see how we can't create a Fire/Ground Pokemon that
ISN'T restricted by the movepool, stats, and can have a more flexible concept than a Camerupt EVO in CAP.
CAP can do anything and everything that EVO can do, except better. The only advantage is that we save time, and that is unecessary if we're going to lose the quality of the Pokemon we create. CAP will be more thorough and with more freedom to accessibility, we can emulate a niche from the lower tiers rather than evolve a Pokemon in order to do so.
Another reason not to do this is the effect it will have on the UU or LC metagames on the CAP server. We have a lot of people who play UU, especially with the advent of the combination with the BL tiers. We have an LC ladder, the only server with any emphasis on LC at all. Because of this, if we happen to choose a Pokemon that is already OU or high UU with a single evolution, we will essentially kill those metagames.
People can use the Dusclops to Dusknoir as the example. Dusclops was already fully functional in OU, but Dusknoir was an improvement on it. If we follow this example, and have something like Heracross, for example, evolved, then it will force Heracross down on the chain and into LC and UU. This is NOT a good thing.
Some ways to avoid this is to disallow OU's to be evolved, to ban them from the lower tiers, etc., but my basic point is that EVO will create a mess. There are too many extraneous requirements for it to be done as efficiently as CAP.
tl;dr CAP is a better version of EVO because you don't have to deal with as many useless things.