What they mean by "change the damage calculations of tanks"?

[Alahra]

All I wanna know is if I should be buying fending accessories or not.

With what information we have available, I would be willing to bet that yes, you should, unless they intend to remove Fending accessories entirely and just give tanks Need privileges on Slaying gear (which is highly unlikely, as that would mean 4 players in a standard eight-man rolling on the same accessories, which isn't a great state of affairs either). I'd imagine their end goal is for tanks to be seeking Fending accessories as they're meant to.

Maybe once we get more information that bet would change, but I'd say it's highly likely that you'll want them at the start of 3.2.