[Bouke Vahl] “eer, what is unsafe about the original approach?”
There are three problems with your idea. Firstly the timecode needs to be transfered to the camera. This means a either cable from the laptop to the camera or a radio link. A cable is cumbersome and a radio link risky.
Secondly, as you pointed out, every take has common timecode. This is a poor practice.
Thirdly timecode should be synchronous to the video frame. Using a laptop to play a QT file means that there is no way to genlock the playback to make sure the camera is getting LTC that is frame synced. Again this is poor practice and may cause the camera timecode to glitch.