Now my commando is my alt but I would think the 5 in Singularity would be better used in Nebula. Damage wise it seems like the better choice. I only second guess the Cooldowns, and how it effect your combo rate. If that creates a significantly greater amount of damage then yea, but Nebula seems like a better choice.

Well > Nebula > Stomp > Breaker

Does Growing Rage effect each tick of Nebula? If so it is definitely the better choice, I would think.

I might have missed it I will reread the OP and other threads but does the rifle really outperform the AoE splash of a cannon? Wouldn't it factor into the build?