1) We're reading this from Kyp's point of view. Aaron Allston specifically states later that this is Kyp's perspective we're getting, hence the more powerful than Luke comment.Kerneth wrote:Enemy Lines I: Rebel Dream, p. 238
"Luke Skywalker had done this once before, a couple of years ago. He'd mentioned it to the other Jedi. No one else had tried it because it had exhausted Luke to the point of collapse, and Jedi were seldom in a position to survive a technique that exhausted them so completely."
"...he didn't think he'd be as terribly drained as Luke by the technique. He was stronger in the Force than Luke Skywalker. He'd known that almost since they'd met--that he had more pure power than the legendary Jedi Master. But this was, perhaps, the first time he had been able to say it to himself without a little thrill of pride. He was just stronger, and that was all. It usually didn't matter. Now it did."
Where does Allston say that Kyp just *thinks* he's stronger than Luke? Kyp seems extremely confident of that fact here, and he doesn't say Luke "trained" them in the technique, he says Luke had "mentioned" it to the other Jedi. There's a big difference between being "trained" in a technique and remembering that it was mentioned as "something you can do in a real asshole-puckering emergency when you have no better options."
2) Remember that Luke has been trying *not* to use the Force like Kyp does. I think it's possible that having to manipulate that much raw power suddenly might be a little strenuous, compared to Kyp who does that sorta thing more often. Remember how Yoda seemed tired out by lifting Luke's X-Wing out of the swamp in ESB? Remember how Yoda has been in hiding and presumably dampening his Force usage to avoid detection by Palpatine? I know this is just extrapolation, but it seems reasonable to me.