I beat it without haste on patch 6 and it was alright. The blood of Lathander really helped my squishest character stay alive, though. However, I had someone sneak in to free the Nightsong first thing. I found the Githyanki ambush more difficult if you don't avoid it -- I had one character go down, one almost down, and one to half HP. The thing about my builds is that I make sure the party can still function with only 3 people if need be and that I use spell slots efficiently. Myrkul really tests your capacity to function in that regard.
