as 99% of shaman are pvp, they will most likely want to go for pvp gear it offeres more survivalbility than the 70 bop blue pve sets, aka dungeon 3.

its impossible to compare this set to work out which is more damage effective, but i can almost garantee that its actually the pvp sets, even the season one gear, it has more spell damage on it, not alot more, but what will make a difference is the crit rateing thats missing on the tidefury set.

and then theres the time invested to get 5 lots of each part what ever it was you wanted to go for, best 2 i can see would be helm and kilt as they have pretty good stats, not amazing but not bad. also a small amount of crit. it was hard enough farming for this set when i got my shaman to 70, before all the arena stuff really got serious. I did shadow labs sooooo soo many times for the kilt and never saw it, likewise for all the parts, i only managed to get the gloves and that was it.

and its only a 3% damage buff per shaman, so really you got to ask yourself, do you see many raiding elemental shaman holding onto their tidefury mixing and matching it with t5 and bt gear to keep that bonus?