Most Aikido training is kata-based, and so it is perfectly logical that the nage might not be able to perform the given technique if the attack has the "wrong" energy/flow. It is often said that the Uke selects the technique because the energy/attack/flow that the Uke provides usually leads into a particular technique. This is fine in randori or jiyu waza, it is less useful in kata-training.
Obviously, more competent Aikidoka will often *make* the technique work anyway from long experience dealing with incorrect attacks or *wrong* energy. Yes, the less competent will cry "wrong energy" when they really should just improvise and learn, but not everyone can do that.
Remember, it is a training exercise. And the uke is training their own movements. If the nage is prevented from doing the technique, the uke isn't learning the ukemi that technique teaches either.
IMHO, technique is usually less important than movement, balance and flow. Maintaining awareness of openings, balance and body control while doing the ukemi for a technique is what will keep you safe in an encounter. Good ukemi translates into better movement. A nage that moves well and understands balance can usually take uke's balance better which makes techniques possible. That doesn't mean the uke should be "giving" the technique away - but adjusting the energy to the level of the nage is important especially if the nage is a relative beginner or just someone experienced trying to learn something *new*.
Rest assured, experienced Aikidoka give one another *wrong* energy on purpose just to see what happens, but most of the time they are trying to set the energy *right* for the technique. I adjust my attacks [energy] for a 5-year old child to a competent teenager to an experienced dan to a middle-aged beginner. It is common sense. It is training. We are trying to teach our bodies to move and react in particular ways. You can't learn physics by writing poetry or write poetry with equations.
I hope that helps.
Thank you for the very candid response.
I train exactly how you mention. Good hard Kihon training. Fully conversant at the level of strength given to every training partner I encounter regarding their experience. From old lady to child to Shidan. My face pulling is when an experienced Aikidoka mutter those words. Of course you button off. What does that achieve for Nage, besides letting them demonstrate their technique?. A false sense of security at Yudansha level? Even worse when they close their eyes and the head does a wiggle! We are not playing Tiddly Winks! But you some it up perfectly...."but not everyone can do that" ask for help