I get asked this question a lot, lets roll up the sleeves here for this one.

There's a trade off for sure. The main hand / off hand has the benefit of allowing you a second enchant to further augment it, in this case 40 int. That int translates into additional spellpower, additional crit, additional mana and additional mana regen. While your main hand allows you to carry your big "oomph" enchant.

While some people make fun of a shaman using a staff, sometimes it's the best option for you at the time. I have yet to find a staff that outclasses a good offhand with enchant and a main hand, but if you can't afford the crafted shield or haven't had much luck with an OH drop. In your spreadsheet you show that you're losing 18 int, gaining 137 mastery, losing 70 haste and 52 crit. To me, it's not worth the mastery gained to lose the other stats, but that's my preference.

At the end of the night, it's all about the stats. If you can achieve the stats you need to heal, then it doesn't matter if it's a shield and main hand, a staff or an enchanted fish.