Nope, this is in fact synchronous. It just degrades gracefully when one of the disaster domains is impacted. The main purpose here AIUI is availability, rather than durability.
For durability, you'll indeed want something like 3-way replication. But that's a distinct problem. If durability is your concern but you're fine with the availability SLOs of a single disaster domain, then you don't need regional replication.
For durability, you'll indeed want something like 3-way replication. But that's a distinct problem. If durability is your concern but you're fine with the availability SLOs of a single disaster domain, then you don't need regional replication.