Since we all mine at MC with a static block size the payout should be something like this:
BTC mined (minus his fee) divided by the total amount of accepted shares (all pools together) x accepted user shares = payout
Agreed. We shouldn't be have to seek out profitability differences between servers. The attraction of this pool is so we don't have to follow up all kinds of statistics, i.e. ideal for lazy miners.
Moreover, as this 'ranking' varies over time (with outtages and such) it is becoming more and more of a lottery.
Any differences in profitability over servers should be equalized at calculation/payout time, like you suggested.