Just took out Lumbering Lambert solo... I'm a 35MNK/17WAR, needed the horn for the Purple Belt quest...
Lambert spawned on top of me as I was hunting him, so I Provoke him and hit Berserk, Dodge, Focus, eat a Meat Mithkabob, and activate Hundred Fists. At this point I've been taking a bit of a beating, so I use a Potion and Chakra myself back to near-full HP.
The fight was over when Hundred Fists wore off... I had used two Backhand Blows, and I had around half my HP left (383/737). It didn't use that Great Bleat that I had been dreading... which is good news.
So this thing IS soloable. Just to let you guys know ^_^