with all this in mind, i think the answer to the OPs question depends on which paradigm people operate under:
if it's #2, the 'responsibility' in training is to humble oneself and focus intensely on soaking up all that sensei has to offer/teach; to serve sensei and sempai with dilligence, and to be the best training partner one can be, and to learn with the understanding that one day whatever was learned will also be passed on to others to continue the 'way.'
if it is #1, then im afraid that 'responsibility' disappears...
I don't think those are the only two choices at all. You can be absolutely equal to your instructor in everything except your knowledge of aikido, but still have too much respect for him and the other students to want to waste their time.
Aikido training is a group endeavor. If any member of the group doesn't hold up their end, the training of the whole group suffers. If you don't like the feudal baggage of the traditional sensei/student relationship, then consider a football team where one person doesn't bother to study the playbook, or a writer's workshop where one person hasn't read the work being critiqued.