Some people claim that katakana are harder than kanji. They have a point. The trouble with katakana is that since they’re only used for loan words, you end up not seeing them very much in the course of study. And since they don’t have a meaning, there’s no “hook” to remember them by. Picture a case where every English word that was borrowed from a foreign word – like ennui or schadenfreude* – was written in a completely different alphabet. Might be a little hard to recall letters like z and q, no?
There’s an English sentence – “The quick brown fox jumped over the lazy dog” – that uses every letter in the alphabet in a single sentence. Someone much cleverer than myself needs to make something like this for katakana.
*I coulda picked more pleasant examples I guess?