FWIW when I added the quickstart (#13228), its main target wasn't newbies, but devs that already have experience with other open source projects and want to contribute to CPython.
These people just need to know where is the repo and the bug tracker, how to build Python, and how to run the tests.

OTOH, the quickstart is also useful to newbies as it provides a concise list of steps and additional links that cover them in greater detail.

So there are at least two targets here:
* experienced devs: they know what they want and they are looking for specific steps that will bring them there.  They also tend to skip wordy sections (so no important info should be hidden in a wall of text).
* newbies: they might not know what they want and/or what to do and need more guidance in a more verbose fashion.

I would leave the quickstart as is, and possibly add a separate introduction as R. David suggested.