Re: bad technique vs. resistance
When I trained Iwama Aikido, I met guys, generally relative newbies, who would just bear down with all sorts of muscle. They were extremely stiff and tense, and I definitely got that feeling of someone jamming a technique they knew was coming. Heck, I certainly bore down with more muscle than I should have.
I also trained with a girl who had absolutely fantastic aikido. Her grip as uke was strong -- though I was physically stronger than her, I could not muscle my way through the technique. At all, full stop. When I was uke, I had the same kind of feeling as when I worked with Rob John; she seemed to move me without the slightest bit of strain, right through where I thought my power was, as if she was stronger than me. And she wasn't even very old or highly ranked. She was in her twenties, and I think she was a nidan. If timing, location, and the politics had worked out, I'd probably still be training at her dojo.
So, while the Iwama style of a strong grip that gives nothing away can be done the wrong way, just as the relaxed, non-resisting style can lead to collusion and unrealism, if done the right way it can lead to some pretty nice skills. At least in my personal anecdotal experience.