For the record, I was working off an old set of notes which were possibly incomplete - they didn't mention the CL/MCT detent in combination with the FCU A/THR button. I made a mistake, I put my hands up to it - no big deal.
So correct procedure has the pilot match the "doughnut" to the current thrust level before using the instinctive disconnect button - doesn't seem particularly onerous to me. The FCU button allows for a way to manually ensure that Thrust Lock mode is activated, which seems like a sensible thing to provide.