p.1 #3New Julieanne Kost video : ACR mask edge feathering
Agreed.
Though not a work around I have found that you can create your mask and do normal edits in LRC, then open as a Smart Object in PS. You can then open ACR to re-edit your LR changes and the mask you made now has the edge sliders for fine tuning. If you have to go into PS sometimes to do other edits (I use layers periodically), this flow can be used,