Is this actually happening or just wishful thinking
I don't think I'd say the same for Signal though.
Using several messengers is what enables competition between them in the first place. It's great for the ecosystem. All messages end up in my notification bar anyway, irrespective of the underlying app.
In my German peer group almost everyone is on Signal as well as WhatsApp. (... and Telegram, for that matter.)
Nobody "moved".
To give an example of how inept, my dad recently discovered that iOS Safari has tabs, and he's had a smartphone for close to a decade and uses Safari heavily. I have no idea what prompted them to switch away from WhatsApp, and before that, GroupMe (which they used for a while because it worked through SMS), but they did.
Signal has around 50M MAU.
Telegram has 500M MAU.
Messenger has 1B MAU.
WeChat has 1.2B MAU.
Whataspp has >2B MAU.
I'd say Zuckerberg is the clear loser in this story: what could be worse than failing to catch up with WhatsApp and discovering a new fundamental use case?
Failing, then spending an obscene amount of money on buying WhatsApp, then seeing a considerable part of that money enabling the Signal Foundation and watching Signal eat up the user base of both WhatsApp and the Facebook Messenger. Users are fine.