Maybe what's confusing here is "true durability" but most people want to know that when data is committed that they can reason about the durability of that data using something like a basic MTBF formula - that is, your durability is "X computers of Y total have to fail at the same time, at which point N data loss occurs". They expect that as the number Y goes up, X goes up too.

When your system doesn't do things like fsync, you can't do that at all. X is 1. That is not what people expect.

Most people probably don't require X == Y, but they may have requirements that X > 1.