Uni isnt overly harder... it just teaches you to have a deeper level of communication. With continuers, you know enough to have a conversation with a primary school student. Ext teaches you to talk about (semi) relevant issues, which is around highschool to young adult level
At uni, you learn the japanese nessecary to survive in the business world, and from then on your interactions with other people are how to improve on your japanese. (Correct me if im wrong on anything)
The exams are partly generic. They dont want you to memorise answers, they want you to call on your bank of knowledge to present a coherent conversation/speech.
Having said this you can memorise small chunks of information and use them in an exam. You may have memorised something for one question, then the examiner asks it in a different way. You should know enough to tweak your chunk to present it right. Same with ext. Sometimes you can slip your point in, other times youll have to change it slightly.
Dont waste your time memorising everything, memorise a couple of sentences for each level of the topic... if your examiner only asks you about one topic its good... it means they are probing your knowledge for all its got