Mastery first vs Sb first. A comparison.

and @ russt: I'm not trying to doubt you in this, but it has been a popular argument on Basil, to say that the W.def reduction of SB is spread out over all the hits. So each hit on a maxed SB would receive 1/6th of the damage reduction. Anything to confirm or disprove this?

That's a crude simplification.

Think of it this way. Your damage range is 1000. Defense subtracts 200, leaving 800. Then SB is 80% per hit, so your damage is 6x640.
Without defense, it'd be 6x800, so you're losing 160 damage per hit.

Now say with the same damage range you use Assaulter, and let's also pretend that it doesn't ignore defense (for convenience ). Then with your damage range of 800 after defense, you deal 450% damage for a total of 3600 in one hit.
Without defense, it'd be 450% of 1000 or 4500, so you're losing 900 damage per Assaulter.

You could say it's "split" across the hits, but that's not exactly true. Everything is accounted for if you just straight compare damage percentages. Defense does not discriminate.