The Alliance Raid roulette daily bonus is set as low as it is because the Lv.50 raids weren't considered in isolation.
The base aether for each instance is based on some expected, average completion time. The daily bonus for the roulettes is set so that each roulette, on average, yields 700-800 aether.
The problem with the Alliance Raid roulette is that the average completion time varies wildly depending on which instance you get, with the Crystal Tower series being unusually fast. The daily bonus is set as if you usually get any other alliance raid series.
