Wow, that was brilliantly written! Indeed, they are both hints as in a safety measure and as in a weakness. I think the important distinction in the point your classmate made is this: scientists don't remember every single thing in their field! They refer to other people's research papers and studies for information. Unfortunately, exams require you to know everything beforehand and write it down in a short time frame. In that case, using these mnemonics might not be a choice for some; it'd be a necessity.

On a side note: How do people not misplace the lion/zebra/monkey/cat in the reactivity series one, messing up the order means you pretty much lose the entire thing