That's very handwavy and not rigorous.
> A ton of people would chose the latter just to be in a more important core role.
Yeah, and a ton of people would choose the former just to be in a bigger company with more perks or because they want to work on something other than an IM app.
Who knows? This isn't nearly strong enough to form a conclusion either way.
> the per engineer capita is 20 times better at WhatsApp
Perhaps, but why? You can't say that they got better talent just because they were a startup, because then I can point out all the other startups that don't have such talent.
> I'm betting any of those engineers that had options are very very happy with their current job.
I'm sure they are. I'm also sure they're not oracles who can predict the future. So they couldn't have known when joining that WhatsApp would be acquired for such a spectacular amount. So why WhatsApp over all the other startups? What did WhatsApp do to attract such world-class talent? I'm looking for a real, concrete answer that couldn't equally be applied to every other startup out there.
The alternative explanation, of course, is that WhatsApp just isn't as complex as some here are proposing it to be. Then we don't have the mystery of how they beat every other company in the world at hiring the greatest unknown talent. Rather, they simply timed the market perfectly, probably partially through luck.