While CAP and durability are orthogonal they are very related in actual systems, I don't think it is ok for a system like Redis to assume that users have multi DC replication and/or other infrastructure preventing mass reboots of small clusters composed of a few nodes. Also note that the more nodes in a distributed system are "decoupled" from the point of view of failures (different physical networks / equipment, different datacenter), the more you are likely adding latency.
But the point in the discussion was never that, since synchronous replication by default is already, exactly as you express in your message, not the Redis business, so fsync or not, Redis Cluster is not going to feature "C". WAIT and its semantics ended taking all the attention, because you know, if your work is to show "C" is violated, you tend to focus there, regardless of the system analyzed not claiming to be consistent.
As for Redis Cluster, many places where Redis is used in the right way, in the environments you say people are happy with Redis, would benefit from the automatic sharding and the operational simplicity that Redis Cluster can provide to Redis, this is why Redis Cluster is IMHO a good milestone in the roadmap.