Raith, Kang, and I did the first three bosses last week. After wiping on the 2nd boss a few times, we went back last Monday and one-shotted the first three bosses. We have so many geared toons we get to try things multiple times a week. Haven't tried boss 4+ yet. As for soloing, I've soloed Morchok since before there were any boss nerfs and am certain I could solo the slime boss. Bubble/ball boss would be much tougher imho.