I see post after post where mathematicians calculate profit or loss based on speed and difficulty, but the biggest factor that will get in the way is LUCK, the POOL LUCK has been destroyed by manufacturers and the private farms. Bitmain is a contributor to this as well. The difficulty is rising in leaps and bounds based on network speed but most of the public pools combined hash rate is getting left in the dust! Oh except when Bitmain or one of the other Manufacturers decides to raid a pool by jumping in with a Ph/s or two for a couple of hours while "testing". Crunch the numbers all you want, till you start adding in the Variance and LUCK of your favorite pool, those calculators are meaningless.
Yes, I too have been raped hard by luck over the last three months, but this is independent of hashrate distribution. Slush has had a 1 month luck of 107% while BTCGuild has been at 91.9% even though BTCGuild is 2x-3x larger than Slush by HR.