I don't think this is necessarily accurate. There's a great piece somewhere by George Ledyard (I'll see if I can find it) in which he writes that he can throw a yokomenuchi that even O-Sensei couldn't shihonage. Anyone can, if they know what technique is coming and set out to thwart it. That's not being realistic or difficult; that's creating a situation built on the premise that the attacker can read the defender's mind and the defender can't alter his course of action. Obviously, there's not much use to training for that scenario.
I myself used to work with an uke who, knowing that a kotegaeshi was coming, would stop his tsuki short and plant like a statue to deprive me of any momentum to work with. He would smirk at this as if he had beaten me, but the truth is that he had just performed an incomplete attack that (a) gave me no reason to defend myself and (b) left him open to all manner of attacks.
There is absolutely such a thing as a bad uke. Just like nage, uke has a job to do, and if he does it wrong, there can be no technique.
Anyone can dream he surpassed O sensei; there is nothing wrong with this. It is excellent motivation to continue training, and in reality we will never know if it is true or not.
I didn't talk about ‘reality' of attack.
Any attack is simply an attack -- categorization (good/bad, competent/incompetent etc) has no sense, it reinforces the false duality in our mind and prevents efficiently reaching the goal of aikido training…
Yes I strongly believe it is quite possible to do efficiently a technique even if attacker knows what technique is coming. In aikido context is very easy because attacker is not countering your technique. And even in judo (with active countering) it is very common.
That is why I think it is a cheap excuse.