Hi MEB,
Thanks for your reply!
I think the separation of Photoshop and Lightroom as two separate products predominantly has historic reasons. When the first Lightroom version was released in 2007, photographers liked the innovative GUI and workflow concept especially compared to Photoshop, and some people couldn't wait for Photoshop (which dated back to 1990 and has become a big old lady since) to profit from this fresh Lightroom approach as well.
Adobe has not really done that, instead the basic, complicated principle of ACR within Photoshop remains - fine from a graphics designer's point of view, but unfortunately from a photographer's point of view.
Without Adobe's historic "ballast" it would certainly make sense not to stick to the Photoshop concept too much but instead find a way to serve both groups of users with a single piece of software without having to swap between two programs. That would be revolutionary!