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.
Another approach is to unset the option "Open Object on Single Click" on the Database > Object Viewer page of the Preferences.