Which of these protocols is better in scalability?
In terms of security, QoS and LLN are only small differences. It would even say, they are very similar to each other.
But how is the performance in terms of transmission style? Is there a relevant difference in scalability between Publish/Subscribe and Request/Response?
I don't think, there is a easy answer, nor a fair one. One aspect of scaling maybe the distinguish between "hot" and "cold" data (say "hot" you must always fetch from the single fresh source (hardly scaling), while "cold" could be duplicated and deployed and may not be fresh (easier scaling)). REST (request/response) I would consider to support also "cold" data (e.g. a lot of html content is just static resources), while for pubsub it seems to be not that common. Anyway, if your application doesn't benefit from "cold" data, then that will be not the difference.
