I don't think too many startups outsource. Certainly not the type that YC funds, and certainly not development which is where you would hope to gain an edge.
The issue with outsourcing development is that to judge the quality of the outsourced job and whether it satisfies your requirements, you have to be competent enough to build it yourself. But if you could build it yourself, then you wouldn't be outsourcing.
So if you can, build it yourself, and if not, then hire somebody who has the skills that you lack. You really only should be outsourcing urgent one-off things and highly specialized non-core areas like PR and legal.
The issue with outsourcing development is that to judge the quality of the outsourced job and whether it satisfies your requirements, you have to be competent enough to build it yourself. But if you could build it yourself, then you wouldn't be outsourcing.
So if you can, build it yourself, and if not, then hire somebody who has the skills that you lack. You really only should be outsourcing urgent one-off things and highly specialized non-core areas like PR and legal.