Good chance Sonnen is just talking garbage. Sounds like Brooks doesn't even know his weight class yet.
Kos's last 3 losses, Hendricks, Lawler and Tyronne Woodley... those are all respectable losses. I think if he faces anyone outside the top ten Kos beats them.
We'll see how he fares against Ellenberger, as a good 'elite' gatekeeper he should be able to take care of business.