This has been discussed here many times before.
I urge everyone who is interested in the topic to watch what top players actually do.
Players as diverse Allison Fisher and Nick Varner have two distinct strokes.
1. For soft shots, the upper arm does not drop at all. That would be shots like the lag to see who breaks.
2. For power shots, such as drawing the cue ball the length of the table, the upper arm drops by about its own thickness -- maybe 4 inches.
I don't drop my elbow on soft shots, just like Nick and Allison. I do drop my elbow a little on power shots, just like Nick and Allison. I was never taught this -- it developed naturally over 60 years of playing. I suspect nobody taught Nick to do a particular thing with his elbow.
I have tried keeping my elbow perfectly still on power shots. It hurts the arm as the arm closes at the end of the shot. Just a few inches of drop relieves that binding/hurt.
Some coaches are teaching purposeful elbow drop. I think Johann is one of those and that Fedor is a product of that training. Fedor has a wider range of strokes as far as the elbow goes. On some power strokes his elbow drops maybe a foot. This gets a foot of follow through which is far more than you are going to get with only a little drop. But on softer shots he has very little elbow drop. Here's Fedor -- watch what he does:
I think that for people who are learning the game it is better to have a stroke that returns the tip to the point on the cue ball that they have addressed. Hit where you have lined up. Yes, there are champions who address one place and then hit another -- I think that's bad practice for beginners. To hit where you have addressed the ball, the elbow has to be in the same place at address and at contact.
Now that you have watched Fedor, does his elbow move between address and contact?