Hi Susie! I just purchased a new-to-me Bernina 770QE and so far I love it too! Such a different machine than the Juki straight stitch.
I've been watching a ton of YouTube videos and reading the manual/mastery workbooks... definitely lots to learn. And I am certain the dual feed does not replace the walking foot. The dual feed is engaged with 'D' feet in order to facilitate better fabric movement over the 9mm feed dogs - used when doing all sorts of different sewing/stitching.
The walking foot is used on the bernina just like (when) you've used it on the Juki - i.e. with lots of layers to keep it all feeding evenly. I haven't purchased the walking foot for the Bernina just yet but imagine I will at some point. I'm right with you thinking my Juki and it's walking foot may do much of what I wish but as I get to know the Bernina better I can see why I will want the walking foot for that, too!
Happy Sewing!
Christine