While Service is 3ad safe, Port isn't. I'm referring to client part.
It's a problem to achieve better performance in a concurrent environments like Wise/ESB.
While it's still possible to invoke Service.getPort() for each call it still not achieve good performance since getPort isn't so fast doing a lot of things under the hood.
AFAIK referential implementation have Port 3ad safe and not Service, that would be good for our purpose, since Service.getPort would be good to be invoked in a 3adLocal manner and then Ports cached and reused.