The top talent you describe is highly unlikely to take what is almost certainly an inferior compensation package at Reddit as compared with places their talents will be better recognized (financially), if compensation sufficient to rent in S.F. is a concern for them.
Yes, SF is crazy expensive and it makes effective compensation smaller. Still knowing that, companies choose to locate here, companies send buses here to help hire San Franciscans, and Reddit's board feared that an HQ move to a neighboring city would lose employees. Those are all strong indicators that desired talent likes to be in SF.
