There is no definite reason for PL rendering every image in the “current” folder - that’s just the way that it was designed/written. It could work differently, as you describe, via a user preference setting.
Perhaps you could suggest/request that behaviour via a “Which feature do you need?” post.
You mean, the “which feature to you need to remain ignored”-bin? 
Are there living witnesses of features requested and become reality?
In DxO PL you just need to select the images you wnat to have synchronous edits to from one basic image. As you work on the basic image, the other selected images also get the edits simultaneously, without the need to first copy, then apply the edits.
But you’re right, Aperture still is - years after it’s death caused by stupid Apple managers - still one of the most intuitive converters and DAM I know of.
Yep - that’s the one ! 
I’m sorry John, some behaviour of DxO really triggers my irony-gene. I try to remain silent because sarcastic comments won’t change anything. But the forum has a function like “which feature do you need” and all what happens is - nothing At least “nothing bad” as well, on the bright side. It’s a pity.
One needs to persist … I have had some (albeit, limited) success in doing so.