I think what you’re not taking into account is that your rewards are totally random, and can only be assessed after a long period of time (and also for the mining difficulty to stay EXACTLY the same).
Take for example myself. I have used many different pools. Currently right now, I am making more per TB on the 50-50 pool because, for some reason, I am hitting blocks much more frequently than I statistically should be.
Many people refer to Burst mining as entering a lottery, because it works very similarly. If you bought a lottery ticket from two different stores, and got a winner at one of them, does that mean the other store provides less winners overall?