>He suggested I open with something along the lines of "merge two sorted lists".

We (my team at Amazon) don't start with a softball, but we try to make sure every question can be down-leveled if someone is struggling. My current one degenerates to: "insert numbers in a sorted list, then find the index of a number in the list". A surprising number of people struggle with this.

I know lots of people get tripped up by graph and tree problems (myself included) because they don't use them in real life often, but simple lists are another story. At FaceGoogAzon scale you can't always rely on array.sort().