If your Starsurge hits for 140k which I belive it easily can without having the starts to allign next season, you'll be giving up 17k damage on 1 hit? If it its harder, it will be even more.
Adding 12% mastery is not the same as doing 12% more damage in eclipse. I could have the exact numbers wrong, but I believe we start with +15% damage in eclipse, then mastery is added. If we're talking about going from 24% to 36%, in reality we're going from +41% to +53%. That's an 8.5% damage boost, not 12%.
So the 140k starsurge would hit for 151k. I think it's possible a super explode-y boomkin playstyle could work, but haste is fun.