Except this fine feathered fellow maintained it's abiltiy to run down prey while at the same time evolving grinders and not the gut to go along with them. If it was transitional, it was transitioning between being and not being.
Or the ability to run from predators. Gazelles and ostriches are quite fast also, and when was the last time you saw one of them take down another animal? ;)
...while at the same time evolving grinders and not the gut to go along with them.
It happens. Pandas don't have the gut for being herbivores either - their digestion is horribly inefficient when compared to, say, cows. So they make up for it by eating enormous amounts of food, relative to their body size. Just because some adaptation would be advantageous, that doesn't mean you'll develop it - it's all in the luck of the draw.
Which may be why it's now extinct. There's no evidence that this was a particularly successful creature.