is there such a thing of having a too big vision?

no but not every situation is a “focus on the big vision” situation, which is commonly when it can seem too big. big vision requires dissection and big understanding to be stewarded well. the Merkle Manufactory team are adept at this

sorta? You can only execute on so much. Though I suppose that's more of a strategy question. If you mean by vision, having unique insight into the future, then the more vision the better — it's only a problem if you pair that with bad strategy

Nah. Big isn’t the problem.

But can it be clearly expressed or is it just grandiose in its vagueness?

Absolutely if you can’t constrain it and deliver on something more realistic along the way