I'm sure I can do better than this so I'm pretty sure you can get him below 40%.
With a good tank gear, Omnotron HM should be doable.
Chimaeron has been killed but it was before the Vengeance fix (and the Avatar nerf.) It's still doable, but harder.
Anyway, I think more bosses could be killed, but we don't really have any Mione. It takes more time to warriors to try bosses and put enough efforts to kill them.