It seems to me that the real point you are trying to make is that the quest rewards should increase at higher leagues. Currently the same, relatively large reward is available for completing the quest at any level. The only solution with giving out packs would be to give out even more than 1 pack for completing quests at higher leagues, but that would be far too much.

The solution then is to give out portions of a pack at lower leagues, which is not possible now, but may be possible in the future.