Fair points, the geography/margin angle is real. Two bits of nuance:

In a lot of those "poorer" markets WhatsApp isn't cheap-SMS, it's the actual commerce channel. People browse, ask and pay through it (India, Brazil, Indonesia, MENA), so even on thin per-message margins the volume and conversion are way higher than email/SMS ever hit there.

In richer markets it's still dominant for messaging across most of Europe and LatAm, RCS is still fragmented (Apple only just added it, carrier support is uneven), and email open rates are a fraction of WhatsApp's. So I'd push back a bit on "everyone settles on email/SMS."