For iPhone only users, so right off the bat your product is targeting 50% ish of a companies customer base. And the non iMessage people get a worse experience?
China/India are like 30-40% of the world, and they are both under 20% usage.
Europe - 60/40% split for android
US/Canada - 40/60% split for iPhone
Even some of the higher countries are only 70/30% for iPhone.
Ignoring that is fine if your target is rich North Americans.
But you are still chopping off X% of customers.
The OP has said they have fallback to SMS/RCS.