Before you continue experimenting with xp. You should keep in mind, that the current xp amount of the quests is fine in my opinion, the real problem is when you use hundreds of multipliers with the elixirs, x2 mini event, pets hb, items, awaken, etc. This causes quests to break and give millions of xp when delivered.
To fix this I can think of some solutions:
1. Some elixirs, items, pets hb, x2 mini event, may not count towards delivering quests.
It could be all or just the x2 of the mini event, or just some elixirs. In the past they worked like this, without so much elixir, you would deliver quests and upload some experience.
2. Only halve the xp given by quests.
Leaving quests completely useless is a mistake, quests make the game fun, receiving good amounts of xp makes sense to do them. Without that xp, why would anyone want to do those quests?
