Yes, the default was changed from "batch" to "no linkage" starting in r14.0 GA, I believe. As you pointed out, you can set the default in the user session, but not globally, and I can confirm there is no configuration policy to change the default internally in the product.
Interestingly, for RAC job containers, there is a configuration policy where you can set "batch" vs "no linkage". But unfortunately the same does not exist for normal job containers.
This needs to be posted on the IDEA section of the community, for others to comment and upvote, in order for a configuration option to be added.
-Brian