You have no idea what you are talking about. The max temperature difference you will see in probably any watercooling loop would be around 3 - 3.5ÂºC, but not more (unless you have VERY extreme loop, that is).
So, please don't spread false information. Temperature variation within a loop is very small; in a normal basis we are talking about less than 1.5ÂºC comparing the hottest and coldest point of the loop.
Tldr: you're wrong, let's see empirical data from testing that proves you right, because actual data disagrees with your armchair scientistry