You already said the pump failed. What's the question here?

'cos everyone is trying to convince me that buzzing/grinding is a sign that the pump is OK but blocked, - the problem might be a blockage behind the pump which would stay there after pump replacement. Also, there is a video out there which says that a failed pump has an impeller which moves freely. And that there being pressure between quadrants as you turn the impeller is a sign that the pump is actually OK.

But YOUR point is more valid. If the pump starts to buzz/grind for anything more than a few seconds and water stops being pumped through, the game is up! Especially if there really isnt much in the filter area and I can move the impeller between quadrants, indicating that no BLOCKAGE is stopping the impeller from moving.