RIGHT!
Make ath scale like MW. So 1 ath give a 5% speed boost, 2 gives 6% 7%,8%,9%,10%,11%,12%,13%,14% that way the 12/27 has distinct speed boost against the 24 agi char. Which means archer hunters and horse hunters will really be able to move, and the difference between the 21/18 str balance build will be pretty big.
21/18 with 6ATH = 45% boost
18/21 = 56%
15/24 = 68%
12/27 = 81%
Now it might be too much of a boost over all so perhaps the base couple points of ath should be lowered a bit, so maybe it should start 2%.