Uke shouldn't move unless moved; ukemi really should be an attempt to regain a stable posture from which to fight back.
I have been taught and train a little differently - unless I am reading you wrong, which I admit is possible.
Most aikido training (outside of kaeshiwaza and jiyuwaza) is kata; uke and nage each have a role to play.
My role as uke is to provide the energy, in the form of the called-for attack, that nage uses to perform the called-for technique.
I agree that my attack needs to be a good attack in the sense of my ending posture being stable unless nage has disturbed it (drives me nuts to see an uke complete a strike by throwing himself into a roll!).
But if for some reason nage has stalled out, my role as a training partner is not to also stall out so we just stand there - my role is to continue to provide input/energy by pressing the attack enough for nage to try to find the correction he needs to get back on track to take my balance and complete the technique. May not always be possible of course and depends on skill level of nage, but that's how I look at it.