Re: If you disagree with your instructor's explanations...
Szczepan try this experiment. Find the most experienced instructor you can find -someone you're convinced has the goods. Tell him you're going to attack, say shomen uchi. Then place a wager. If he throws you irimi nage he gets $50. If he doesn't you get $50. If you were to genuinely run that test I doubt he'd irmi nage you -whatever his skill level.
Thats not to say he's no good - the point is it's easy to counter when you know the strategy.
Ah you say but he should be able to blend with my counter into something else.
Sure but then he's no longer demonstrating irimi nage. So a simplistic "can you counter the technique" argument doesn't work when we're talking about a paradigm which is asking uke to "behave as if" they didn't know what was coming for the sake of learning individual techniques rather than sparring continuously.