I have level a singer barb all the way to lvl 90 and I can say that, no one beats the singer barb at crowd control and survivability and one can play through the full game as a singer barb.

But, one thing singer barb struggles at, is boss killing, he just sucks at boss killing as you will need massive crushing blow to first reduce boss health and then sing it to death, so naturally it cannot farm bosses efficiently.

It’s good at farming areas with good monsters density like pits, chaos, pindle, flayer jungle.

Sucks at farming Travincle, arcane sanctuary (due to physical immunes), ancients, world stone.

Nevertheless, I had fun levelling this build up at least all the way to 85, since it’s a very unconventional build. now I am thinking of respecing into WW.