Scalability is very subjective in this context. What I meant was, it requires an admin to create static queues/topics well in advance and maintain them administratively, before you can actually use them. This is in contrast to dynamic destinations, which could be created on the fly at runtime, enabling you to add or remove JMS resources dynamically, thus achieving better scalability. Hence it is not so much about load factor (number of messages a resource can handle) or taxing the system's performance due to the usage of static destinations.
Thank you for your time and I hope I answered you question.