Because the person who made the list doesn't understand corruptors? (Or the current meta?)
Fire, Ice, and Beam are great corr primaries. Cold, Dark, Sonic, Poison, Rad, Time (and as you mentioned, kin) are all great corr secondaries.
There's a reason the TF olympic teams use corruptors. (They're really good!) If anything, the most valuable ATs at the top end are Blasters, Corruptors, and Scrappers.
I agree that Brutes are kinda useless. Especially since Tanks now can take aggro off-of them with ease, and Scrappers do more damage.