I think there's a bit more to it than that. Doom as a series is known for its difficulty. A lot of the people having issues already played Doom 2016, which wasn't exactly a cake walk. It's not just that Eternal is difficult. It's about why it is difficult for some people. I think a lot of it is that it looks like a duck and quacks like a duck, but it isn't a duck. It looks like a classic FPS, it looks and controls like D16, but it's a totally different beast. If you play it like you're used to playing shooters, it will be very difficult for you.
The Marauder really threw me off because until that point, the game was about running and dashing and double jumping and flipping off monkey bars and teleporting, but then suddenly you're locked in a small room with an enemy who plays like a Darknut in Zelda or something. The lesson Eternal preached before this was: keep moving or die. Then it became: stay locked into medium range of the Marauder or die. It was like a hard shift into a totally different game, and all the skills and tricks I picked up before were useless. Which is actually a cool idea and great way to add some contrast, but...man. Fuck that guy. Lol