I wouldn't worry about the Sigma 50mm all THAT much. It's a heavy lens, but not all that long. Part of the reason people mount long telephotos to the tripod instead of mounting the camera is that they are very long, with huge, heavy front elements a foot from the camera. The Sigma doesn't come with a tripod collar, and the front of it isn't any farther from the back of the Z7 than it is from the back of a D850 by definition - the distance from any point in the lens to the sensor is the same for any compatible camera at a given focal distance, or focusing wouldn't work. That's why the FTZ adds length - that distance is shorter in an unadapted Z7.