If uke is just a crash test dummy, and doesn't manifest the same aiki, etc., that nage does, how can uke ever counter nage (kaeshi waza)? If half the time you're training aiki and preserving your balance (nage), and half the time you're just performing some conventional move/attack and/or giving away your balance (uke), how can you progress? Perhaps we just understand aiki differently, but if I were to preserve the uke/nage training paradigm, I would have both uke and nage apply the same body/mind principles all the time so as to condition the body/mind more efficiently. IME you can still have a martial encounter within these parameters.
I'm certainly not saying that uke should be going through the motions or giving away their balance. That's not what I mean at all. What I am saying is that if nage is practicing shomen-uchi ikkyo, then uke should be trying to hit nage in the head. IMHO this is not particularly 'aiki'.