I will just quote the paragraph that went with this photograph, as I cannot say it better.
"Love, love this Picture! This horse is engaged, proud, part of the partnership. Rider and horse focused together. Poll high, ahead of the vertical, open throat latch creating a beautiful upsided down u not a v shape, long beautiful neck. This horse can breathe!
Look at the position of the curb, something you hardly ever see anymore, usually it is fully engaged and horizontal with the ground even in walk.
Look at the tail not swishing but naturally raised in as proud an arc on the back end as the horse is on the front end, showing how the spine is fully engaged from the front to the back."
Now to compare a modern dressage photo:
I can see the differences.
What you see wrong in Western Dressage is just as obvious in USDF/FEI dressage. You just have to know what you're looking for.
I'm actually reminded of Anky can Grunsven, considered a top of the line (modern) dressage rider. She stepped into the reining world, and she gets bashed so hard on youtube and forums alike because she's suddenly considered unable to ride. Watching Anky rein, personally, I think she is very unbalanced and not at all precise. Now, when it comes to watching western riders, I pretty much only watch Clinton Anderson (whom takes dressage lessons, btw). To me, he's very balanced, his horses transitions are very smooth, his signals are clear and performed with precision.
I do seriously and honestly believe a horses performance is based on their rider and said riders ability to balance.
I would think that a good, balanced rider, and a good, balanced horse, should be able to transition between the different disciplines with very few problems and perform any maneuver at any time, no matter what tack they may be wearing.