I'm not sure what Tyler's problem is, but I don't think it's that Dianne doesn't know how to crack the whip, or use posture-correcting tools. Here's her whipping a borderline duffer into not-too-bad shape on DWTS AU
I think the height difference does mean that his posture can't improve much more in the ballroom. I'm not sure why so many celebs struggle so much with this. You see it every time with tall blokes, the judges keep saying 'stop trying to dance down to her, she can dance up to you' and most of them just can't seem to manage it for some reason. It's obviously never an issue when pros with large height differences dance together, but I guess it must just be something that takes a long time to get right.
Similarly, I've noticed that a taller female pro dancing with a shorter male pro looks fine, but it always looks awkward when it's a celeb. I really noticed it last year on the American one with Amanda and Alan. She was about the same height as him in low heels and there was just always something slightly awkward-looking about them, even though she was a good dancer. But Luba and Nadiya can dance with Gorka without it looking weird. Maybe it's just something that can't be sorted out in a few weeks.