There are network effects regarding the portion of outliers that SV captures, but if we're talking about experience alone then I'm skeptical of your claims given how much of SV is driven by freshly minted CS grads.
Where else in the world can you hire the guys who solved exactly the same problem (Monolithic Rails Stack) at companies like Twitter, Airbnb, Zendesk, etc.?
You're making a big assumption, which is that all those good engineers love to live in Silicon Valley and want nothing more than to stay in the area their entire lives. For each one of the engineers who feel that way, there's someone who worked here for awhile but now dislikes the area for one reason or another. Enticing good people to spend a few years in Berlin working for a company like Soundcloud might be easier than you think.