TOS was labeled "optimistic" only because it did show a future where somehow humankind got through it all (kids, let me tell you about the 1960s), solved a few major problems, and seemed to be able to get along well enough to cooperate for a greater good.
It presented a better
world, but never a utopia.
And, while Earth may even seem
like a paradise full of comfort and no worries for its 23rd century inhabitants, I have a feeling Cumberbatch is about blow that myth to bits and show how naive and complacent that attitude really is. (If the destruction of Vulcan and probably being just minutes from Earth's own destruction didn't destroy that myth, already.)