Random similar data point. I very recently asked a P1 coworker to call about a seat assignment oh my behalf. They got the exact same line.
Granted, I was asking for a seat I was not entitled to (forward cabin on A380). But rather than getting a “no, because that’s not allowed,” they got just what you said: “sorry, we’d love to help, but we can’t! System won’t let us! So we’ll make a note. Ok bye!”
What a ridiculous request. The agent was absolutely correct, they used to be able to override the system but they now can't. So in this instance they agent was 100% correct.