Think about it - There's been a lot more research done in the department of human nutrition than avian nutrition; but there's no human pellet out there.
And fer real? An amazon parrot from South America has the same dietary requirements as a cockatoo from Australia as an African grey from Africa? If not, why the same pellet for all of them?
Don't get me wrong, I feed pellets; but I view pellets as more of a vitamin pill than a complete diet.
I think it's lazy to feed only pellets; just like it's lazy to feed just bird seed.
Feeding Your Bird for Health
Diet
Why Food is Better than Pellets
Thoughts on Diet
Parrotlets and Pellets