Rather than having XP and star rewards give you nothing when you are maxed out for a certain mini, you should have all rewards give you at least arc energy. Some XP rewards give you arc energy when you don’t need the XP, others do not give you anything. The same is true for stars. Sometimes a star you don’t need gives you arc energy, other times they give you nothing.
Getting nothing from a reward feels bad. Also, it seems like XP rewards always allow you to pick a mini that needs XP. Star rewards do not do that though. You will end up picking from minis you do not need stars for while minis you still need stars for don’t show as an option. In both cases you don’t always get the arc energy when selecting a maxed out mini. Sometimes it gives you arc energy and in other situations you get nothing.
Because you don’t get the rewards in certain situations it means doing certain quests and event challenges is pointless even though you are still trying to progress with upgrading minis using arc energy.