I can second that, 2 devoureds in a DE mission solo yesterday. I'm a tank, built for it, but even I get nailed pretty good by them, and damn slow to kill purple bosses now.
Not complaining, I like the new challenge.
Oh - and have you read the posts about the mission experience NOT being the same for two team members after they exit a mission set on invincible? Might be other settings as well. Had a partner today, exited, I got 6000xp as the mission holder with invincible, she got 12000.