If the air ambulance flight had used the terminology “cancel IFR” when they were on the visual approach, can you explain if I would have been held under those circumstances? i.e. two VFR aircraft. I somehow think not, but there is no leadership shown in telling aircraft when it is sensible to cancel IFR so traffic does not have to be held in risky circumstances.
That's it, isn't it Dick? An IFR aircraft that probably wants to retain the protection that IFR status affords has to change to VFR just so you can go on your merry way. Have you ever thought that the other pilot may not be able to see you and so will not accept VFR? Or that he might be getting busy for the approach? Or that his pax didn't deserve it?
I can tell you there are two chances of me changing to VFR just to facilitate you (unless I can see you and you do what I require): None and Buckley's.