So while it's not quite 2685, the optimal amount of haste rating for Destruction is slightly higher than you're saying it is.
Where did u get that 2685? As far as I know the "haste plateau" is at 30% raid buffed, which is 2437 for goblins and 2589 for others, with full haste buffs from raid, i.e Dark Intent and shaman's totem/moonkin aura/spriest aura.
So no, you don't need shaman if you have a balance druid or shadow priest, they give the same haste buff as the totem.
edit: Is that 2685 some plateau for BL to reach next tick(s)?