I agree with other replies here with one addition. People who get into grad school are generally the high achievers from their high school and undergrad programs, so they are used to being the only or one of few star students. In PhD programs everyone is a star student, so it can be a bit jarring to folks used to being head of the class when they suddenly aren't.

It can cause a bit of jealousy and competitive thinking but most of the time students get past it and focus simply on enduring the gauntlet.

Getting a. PhD isn’t super competitive (speaking from the US), but if you aim to get a professorship at an R1 it’s somewhat competitive across the board. The program coursework vs undergrad depends on the program too— I would say most differ somewhat substantially though. For most humanities degrees you’re doing coursework for 2-3 years and teaching undergrads while you prepare for qualifying exams, then you teach and write your thesis for a few more. The graduate courses are often in seminar (circle discussion) format rather than lecture.

Definitely not the same, at least in my experience. It differs by field, but in my field, grad programs basically have zero classes, and whatever classes there are are generally automatic A's. In turn, the difficulty comes from the fact that you are basically in indentured servitude to your advisor, and there is no actual recourse for trivial things like "overwork" and "burnout."

I know of people who did 70 hour work weeks, and for a period of time, I had to do that as well. Also, you get paid less than you would if you had just gotten a 40 hour per week job at a company.

Anyways, the advisor that you pick really makes or breaks your experience.

Depends on the program. Diploma mills for graduate degrees absolutely exist but many are extremely competitive.