Dont know the batch size for reference but 1/2 an ounce as a flame-out addition doesn't seem like much. The last brew (10 Gallon batch) I used these hops in had 1.0oz @25min, 1.5oz @10min, 2.0oz at flame-out for a whirpool and 2.5oz for dry hop. Amarillo wasn't the only hop; I also used Chinook and Cascade but there was a significant qty of Amarillo!
The brew was delicious and wasn't grassy at all nor did it have any odd flavors like garlic and such. Maybe I just got lucky with my shipment and/or perhaps there's other things influencing the off flavors others report.
Again, I don't think 2013 was as aromatic as 2012 but it's proved to be a usable hop for me!