... Well, that's not been the case for me. In any case, I finally beat the mission with only henchies, though surprisingly, it was a piece of cake the last time through. I switched to a R/Mo and am now using a Bow and Judge's/Barrage. Probably a result of me not only timing my Distracting Shots/Savage Shots well against those Chain Lightnings/Thunderclaps but me getting a bit more skilled. Time to try out Thunderhead with henchies.
I guess the consensus is that it is
not possible to solo the whole game by yourself. Well, I think it can be done. With a lot of patience. After all, you'll level up quickly (up to a certain point, naturally), and if you level up enough in pre-searing (the enemy doesn't aggro in groups there and the enemy seems quite a bit easier), then you could go into the next part with a considerable head start.