Thank you everyone for your feedback.
I do have the 16-35 (by accident- long story!) but its unopened as I decide whether to keep it.
I've certainly been leaning towards returning it but one last option was to use it now as an equivalent to the 24-70 portrait (didn't know how successful that would be) and also as a walk around lens and then down the line as a wide angle on a full frame body.
I think there's better options though.
Thanks again.