I do agree that it was---in retrospect---unfortunate and optimistic of MZ to promise too much freedom and independence from FB. But it seems FB _did_ give WhatsApp a long runway, it's been 3-4 years since the acquisition. If their ideas don't work (wrt bringing in revenue in line with the acq. price), at some point you have to go back to square one and do the thing that works (also for IG), and do the FB-style ads/monetization.
I don't have a lot of sympathy for the WhatsApp founders. They took the money (they're worth almost $10B now), they did have 3-4 years to find their (and their team's) way within FB. It's cool that they don't like ads and moral standards or whatever, but come on, you have to be more rational when you're playing in the $10B league.
Disclaimer: I worked at FB previously for a short time.