Alright 10s, school's in. Have a seat and learn about the scaling of your bracket.
From a proportional standpoint, secondary stats from 10-14 scale at a ratio of 2:3:4:5:6. So you need twice as much crit rating at 12 to achieve the same level of crit at 10 (2:4 ratio), and three times as much at 14 (2:6 ratio). Therefore, the scaling of 10 to 14 is 3X.
Level 15 continues the scale, so if the bracket shifts to 11-15, the ratio becomes 3:4:5:6:7, making the scaling of 11 to 15 drop to 2.33X. Going from 3X to 2.33X is a 22% drop in scaling. Both 10s and 14s would gain access to better gear by moving to 11 and 15, but the gear improvement stays linear for both.
Would this nerf players who previously ruled the roost at 10? Unquestionably. Would the nerf force everyone to go to 15 if they wanted to remain competitive? Not even close. Such a shift would simply make the whole bracket more interesting, instead of a bunch of 10s sprinkled with a couple of 14s.
Your homework is to work up a chardev of your favorite class and spec at 11 and at 15, and determine which one, if either, had an advantage. Extra credit if your reply is as snarky as mine.
School's out.