Have you ever read the zen story about the zen master serving tea to the wan-a-be studnet.
Bruce Lee used it in one of his movies....Your tea cup is like your mind, how can you add anything into it if it is already full....
Anyhow, I did switch also to Aikido, 16 years ago, and am super happy about it.
I don't think it's much about technique, but more about teaching style. Like you said, a joint lock is a joint lock, a punch is a punch, how different can they be.
Well, the teacher, with his own individual perspective can teach it in a completely different way, which can really help you understand more of what you've already learned and at the same time, really frustrate you (if your cup is full.)
One great proverb that I always think about, "When in Rome, do as the Romans."