It's not as horrifying as people make it out to be, it's just very emotional and occasionally intense. The movie is not so much about bodybuilding but rather a man's gradual decline into insanity with his bodybuilding career's failure being the pivotal point. This movie does an AMAZING job at realistically representing men's mental health issues from the POV of Killian Maddox, who is on the spectrum, has anger issues and also is depressed. You can feel the raw emotion punching through the screen. The shots and music are curated with surgical precision that conveys Killian's emotion in a very impactful manner. Though the majority of the video is glum, I did find myself entertained and fully engaged for the whole 2 hours of it. It's filled to the brim with moments showing Killian's emotion and thoughts through very subtle expressions without the use of words. This is arguably Jonathan Majors' best cinematic performance yet, and in terms of emotional impact, probably up there with Interstellar.
(And yes, it is somewhat like the Whiplash of bodybuilding, except Killian experiences Terence Fletcher in the form of a chain of events that make him lose his mind over time.)