Item Plans drop very slow. To get a full hope bringer set on 5 heroes is very hard and you level faster then the amount of time it would take you to acquire all of these. Moreover, boss events give you plans only for the top 3 players of the event. This I find bad, because the other 7 people in the top 10 get nothing but their names published. Why not make it so that everyone in the top 10 from a boss event gets a plan based on how well they've done i.e. 1st place gets guardian helm 10th place gets hope bringer. Moreover, treasure chests in the arena drop nothing very interesting. Basically you have the big credit and the big coin, where is the big treasure chest? Another suggestion for the Item Plans would be to have a drop rate from arena treasure chests.

TD;DR Top 10 players in boss events receive item plans not only the top 3. Make item plans drop from arena treasure chests too.