I think we need to clarify what we mean by "poorly attacking." Certainly it is extremely easy to deal with a typical beginner attack. It is much more difficult to deal with an attack from an experienced martial artist from another style. In fact, it might well be impossible to execute a specific version of a specific technique that the person has seen coming and can anticipate. (ie, to be successful in a typical class situation)
Which is exactly why those individuals represent a challenging teaching situation, see my post up above. Even if I'm comfortable with the idea that "I'm not that good," saying so doesn't exactly inspire confidence in a new student unless I can clearly articulate how basic technique and kata practice fit into the development of "real," effective aikido.
I deal with a range of visitors so I will go with poorly attacking as legitimately poor body management choices, not stylistic differences. For the record, I still include myself as making the occasional poor body management decision. Its just when I make a poor choice, sensei dumps my on my head and says, "what would you do that?" And yes, as the technical skill is higher in our partners, the more difficult that interaction becomes. You're felt the heavy ham that is George sensei's fist - he doesn't need anything else and that is sufficiently challenging to do anything
Most of the better martial artists that come my way are exceedingly polite and genuine. They are skilled and BS'ing them just gets a grin and a smile. Most of them also know that you don't get things 100% of the time. Our Hagannah guy is leaving to work for MIT in the fall (George met him last year at our seminar). He was a real treat and someone with whom I would never cross hands. Ever. But, man he was fun and insightful and a great person. The thought of BS'ing him with the "I can't show you aikido because I would have to kill you," stuff would have been embarrassing. Nor was he upset when our aikido had little effect on him. "It's all BS, it's just the system that gives you the advantage," he would say.
I get my feathers ruffled because I don't believe that we need to explain what we do. If we do it right, those with sense know. I fwe need to explain what we're doing, we can improve the way we do things.