Your method actually could make it even more uneven. As you said, if there is an uneven class/foe distributions, you would expect a professor to take all 5 werewolves no matter the level of each werewolf and then the magi only has 3 low level spiders? Whereas, in my method, the magi would take the 3 low spiders and one werewolf so that it's more even. In my method, I take the highest rated foe that my profession can handle best so that others don't get stuck with those, but to even it out, I may end up having to take on foes that aren't within my profession to even out the amount of foes we all take. But evening the distribution of foes and if we all attempt to (at least at first) take the foes that our profession handles and then after that take the lower foes in other professions so that we are all keeping even.

As I said, I always try to take the highest rated foe in my profession's skill set first, I'll always take the extra foe if the number is unevenly split, and I'll take foes outside of my skillset if it's uneven distribution. But if that distribution is 8 spiders of varying degrees and 1 dark wizard, I'm not going to leave the spiders and just take my one wizard.