Starshatter is better.
I was simming it later this day and the results were a rough difference of 800-1k DPS difference.
This is probably even going to ramp up as you upgrade both weapons, i don't know yet but probably you break some kind of point with SS. I'm an Orc myself and i had to forge away mastery.
2 targets is just some "cleave". You will hardly notice 500 more or less mastery anyways. When there are big AoE fights like Wind'lord HC MAYBE. But not at Garalon. Imo the weapon dmg will still outweigh that.
But ofc - if you want to do so, just sim it with 2 or 3 targets and you'll see for yourself. I'm pretty sure SS still comes out ahead.