It's not really that the tasks are difficult in my opinion, just not worth the resources and time (especially this one). Why would I want to raise a pretty much useless purple-blue dragon when I can use the food to get a Diamond or Champion Dragon to level 15? Why would I put in the extra effort when the main prize looks like a Rapunzel that got in a fight with pink paint (including the metal cans)
It's completely possible to grow that much food in the required time for the tales, but with the current frequency of tales you don't have much food left for other dragons. Currently it feels like you're being forced to use specific resources in the game and spend extra time, to me that's losing a bit of the fun and freedom this game offered me in the past.