That's relatively accurate. The only thing that I would change is the middle ring of the triple with the smallest cog. Even that combo should not be a problem. The middle ring of a triple is positioned almost as far to the right as the big ring on a double, so I treat it the same - no use with the largest cog.
The 48/21 should also be useable, at least briefly. There is no exact match for this ratio with the 36. A 36/15 is a little bigger and the 36/17 is smaller.