But this is static training. If we're practicing dynamically, or if we're out in the world, why did nage allow uke to get a strong grip in the first place?
The training is as dynamic as you can make it, I you can move big strong uke from nothing, that's progress. The starting point is static in the case of katatedori, morotedori, katadori and other "doris". It is a laboratory setting where the partners can repeatedly and safely examine the forces in play, the various openings that may exist in their waza, the mental attitude, the appropriate ukemi etc...
I suppose many things can be said about "out in the world" application, just because it is something I read today, I'd quote that "violence is always unpredictable" http://blog.aikidojournal.com/2014/0...-tom-collings/