I understand what you mean, however I disagree. If an OF throws to the plate and the cut off catches it and relays home, I'd say the OF is still making a play on the runner.The real argument, and I can't make a strong case one way or the other, is whether a play was being made (or not) if the catcher's throw was never intended to put THE runner (not an assist to put out some random runner down the line) out. I don't feel it is, but I can't fault you for thinking it is.
The defense has a play on and the catcher is starting that play, so her actions are making a play on the runner.
You'd be opening up a can of worms allow batters to interfere with catchers because the throw wasn't going directly to base that the runner is going. (Think a pick off attempt at first and the runner breaks for second. Can you interfere because that throw can't directly result in the out?)