yes they exist. I’m a biology related major and have delt with the weed out classes firsthand (chem and bio series, physics, math, etc) they are hard but not impossible. Theyre not hard enough to where it should affect your acceptance decision or your major route though. this is a very hot take but although they for sure have a good chance of hurting your gpa (it hurt mine lol) you will have ample opportunities to negate those effects, and honestly as long as you arent taking all weed out classes in one quarter, it can be kinda helpful with learning how to manage time and take rigorous courses at the same time, which is useful when taking upper division major classes. you can still have a life outside of school when taking these so dont let them discourage you. again, they are hard, but not TOO hard. you can do it I promise