$100K won't buy enough professional services to build, launch, and operate an MVP unless the app is very simple. If it's simple enough that anyone can drop $50K-100K on design services and have your business cloned, it's not a very defensible startup idea.
There are occasional exceptions, but typically the founding team must have the majority talent and skills required to launch the MVP.
Please don’t listen to this. You can hire great developers all over the world for far less than $100k.
Using YC’s $125k to hire a few contract engineers to help you reach velocity and deliver a V1 is an incredibly smart move.
Not every YC company is a developer tool or something complex. In fact, looking at the most recent batch I’d say the majority are fairly simple in their technology approaches.
While that's true, it's rare that a YC company at the founding stage is so unique that only the founders can do it. It's not about the simplicity but rather the fact that the founders are basically putting in unpaid labor that provides the moat, because for someone who wants to clone your business, they need to be convinced first that it's worth investing in.
The founders are convinced, and hence are the ones doing the free work.
By looking at plenty of the "Show HN:" posts we can see many examples of more than just "simple" services that were made on a much smaller ( or $0 ) budget.
There are occasional exceptions, but typically the founding team must have the majority talent and skills required to launch the MVP.