Personally, I think that both Hunters and Jumpers can be equally as hard as one another, I have competed in higher levels of both.
Also, is it true that hunters generally have a more arched back because I wasn't sure on that.
Everyone has their own way of riding... In my picture my back is flat. I know many Hunter coaches teach having a arched back, when I was little that's all I was taught "arch your back, arch your back".... terrible for your body, I am 20 and have to go to the chiropractors twice a week because of that.... After that "arch your back" phase, I began riding Dressage to help my Hunter/Jumper foundation, and no you don't need a arched back. But again, I notice a lot of coaches train it, but I think it is improper.
There is a difference between sitting tall and arching your back.... Arching your back causes you to "hover" foward in your seat, versus sitting tall and using your seat bones.