It depends on the environment. "Jack of all trades, master of none" is not necessarily the best possible adaptation. Not all that long ago, there used to be bears in Africa. Not any more, though. Omnivorous generalists like bears don't do as well as specialists in such a highly competitive environment. They aren't as good at predation as superpredators like lions and leopards. They aren't as good at browsing and foraging as giraffes or elephants. And so they got pushed out.
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.