Philip Stoyanov in this post suggested I can use SQL Dev 4.1 to
you can drag tables from SQL dev browser directly to to your relational model diagram
So I gave it a go and I liked it, but I found when I clicked and held a table to drag it to the relational model, the table opened as a tab. So I have to close the tab first, then continue with my drag operation.
Hmm, in recreating this I found a workaround, so I'll leave this up for reference to others.
Put focus on the data model, then click and drag table into canvas.