I certainly couldn't build that in a weekend but nor would I need 9500 people. Keep in mind WhatsApp was running with 50 engineers in 2015 when it had 900 million users. Last year, according to some sources, it had 3000 employees and 2.4 billion users. And that's groups, voice messages, video and voice calls, WhatsApp for business, integrations and a lot more.
Some of these seem reasonable, some not. There is no need for legal presence everywhere or to even have a permanent hire for that. The many clients make sense (including consoles too) but more than 10 people per client? It's not the most complicated app. R&D I guess makes sense too.
Actually, it would be interesting to see the breakdown of employees by category.
Regardless, I think the answer lies somewhere between what you said (unknown at a glance costs) and what others have said - too many managers managing managers and overhiring.
Whatsapp is just sending messages. Here's music recommendation lecture on using latest techniques to better serve users. I am glad that their music recommendations are very good. There are so many nooks and corners in a big company like Spotify where you need someone to be responsible for.
Some of these seem reasonable, some not. There is no need for legal presence everywhere or to even have a permanent hire for that. The many clients make sense (including consoles too) but more than 10 people per client? It's not the most complicated app. R&D I guess makes sense too.
Actually, it would be interesting to see the breakdown of employees by category.
Regardless, I think the answer lies somewhere between what you said (unknown at a glance costs) and what others have said - too many managers managing managers and overhiring.