The relationship between the in-camera histogram and the histogram of the raw image opened in LR or ACR differs depending on the camera model. Once you understand the relationship for your camera, you know how to interpret your in-camera histogram. This needs a bit of up-front trial and error, but isn't by itself a reason for complexified image editing.
Correct and it's really not rocket science at all. I have an X-Rite passport and it was pretty simple to put it up on the brick wall outside my house which has even illumination in the morning hours as the sun is on the other side. I made a series of exposures and was able to easily figure out how to then set my camera for maximum ETTR capture (Nikon D300). Now there will be some scenes which have illumination that needs to be compensated for but it's easy enough to do once you have the basic understanding of ETTR. We also have it much easier than Ansel Adams did since we can easily set our cameras up to take a series of bracketed exposures as needed.