I don't know what others do, but everything that is relating to payouts with my multipool is public. (reference http://multicoinpool.org/index.php?page=statistics&action=round add the totals minus Perfection and Southpaw; testing autotrade together right now.)

I also don't "gain on the difficulty." If it happens to be profitable using math, then that is what is mined. (reference http://multicoinpool.org/index.php?page=statistics&action=profitability )

If other multipools don't give enough transparency I can see where you are coming from, but you are assuming that all are bad apples because there could (not implying there is or isn't,) be a trend with a few popular pools.