In the world of idealistic fantasy, an software defined network of whatever kind would centralize all functions. Pesky reality gets in the way of idealism, and so it is that we find full centralization to be an impractical idea.
Consumers evaluating SD-WAN shouldn’t think of it as a WAN optimization replacement, at least not exactly. These are different technologies, although it might be fair to think of SD-WAN as the successor to WAN optimization. SD-WAN and WAN optimization are compatible technologies, but not interdependent technologies.