It depends on the stage of the startup. Once they've taken enough VC money and have a yearly budget of say $10m, they often just need a certain number of bodies to flesh out whatever idea they have already implemented in their PoC. They don't need geniuses.
Startups are high risk high reward and do unconventional things, hire unconventional talent.
The fact that any startup is taking a faaang approach -
The ceo of a great startup must be the talent detector first and foremost,
If the CEO of startups are not doing the talent sourcing and attracting, what are they even working on.