So, the adventure time style is simple, yes, but that doesn't mean it's fast to do. It's got simple shape language, but those shapes are kept very very on-model (except when they purposely stretch and change, which btw is also difficult to animate well), and it's traditional animation, not flash "puppet" animation. It's a very sophisticated and specific style.
Simple =/= Fast and Easy to do.
Anyways, to answer your question, I think the absolute most that I could do in a week is maybe like, 4-5ish pages, and that's if I quit my job, stopped talking to my friends, family, and girlfriend, only focused on one project, and didn't stop to edit my work. My story isn't worth ruining my life for, and I don't think I would let myself only work on one project, or stop editing my work, so that will never happen.
If I changed my style to be something simpler/rougher then I could do at a faster rate, and started writing a story that didn't take as much thought, then maybe I could get like, 10 per week, but I probably wouldn't be satisfied with what I was putting out.
Mangaka are known for putting out large amounts of work on a daily basis, but they're also known for being overworked, overstressed, depressed or suicidal, and many of them develop arthritis.