but the Forum Jump defaults to the forum that you're viewing so is automatically the same function as the Return to (forum name) new selection
No, apart from the fact that it miles away down on the bottom of the page in the corner, clicking on "Forum Jump" merely brings up the list of forums; if you want to stay in the current forum, it won't react when you click it in the list. It will jump to another forum, but not the current one.
That's why I cheered the reinstatement of the "return to the current sub forum" button, which had disappeared.