I decided to go back and mark up ***** and Totilas so that I could better see the difference between them. I think I agree with you that Totilas is the better conformed horse, but only slightly. He's got a more laid back shoulder for sure, a higher set neck, a longer forearm, and better front pasterns. You're right that he's lighter in the front, and he does not have as high a wither.
However, if he's got more bone it's negligible. ***** has a much cleaner head to neck connection and I think his loins are a little stronger. Totilas is also a longer more rectangular horse overall. You pointed out that you thought that *****'s croup was a bit flat, but from where I'm sitting they look like they have the same angle to them, *****'s is just longer. This may still have the effect of making him more of a leg mover than a back mover, I'm not entirely sure? ***** also looks to me like he's lighter in the front than behind contrary to your critique though the difference is not as dramatic as with totilas.
However, though Totilas is clearly a very very lovely, hugely successful horse, I've never been as enthralled with his performances as some. Personally I find his movement very like that of a saddlebred. He has a wonderfully free shoulder and very dramatic forelimb movement but he doesn't always seem to come through behind especially in the extended trot. And yes he looked this way even with the supremely talented Edward Gal aboard:
https://www.youtube.com/watch?v=k1ttmKBcJfs
He looks like there's a fraction of a second of a difference between when his forelimbs and leave the ground and when his hind legs follow. I also feel like there are horses with better articulation in the hocks.
Because, as you said, ***** was never as successful as Toto, I choose another horse to compare, Valegro, sired by *****. Personally, I think that Valegro ridden by Dujardin is a more correct, if less flashy, example of a grand prix dressage horse. Watch here:
https://www.youtube.com/watch?v=DcDLLxgWa_Y
To me he looks much more active behind than totilas, his hocks move like the pedals of a bicycle, he steps underneath himself more and the timing of his footfalls is the same in front and behind in the trot. To me Valegro looks very much like ***** with with the most notable difference being that he is a bit shorter and steeper behind.
So take what you will from that and please disagree with me on any points on which you feel I'm mistaken! I'm still learning as we all are, and have presented my opinions so that I can revise them as needed.