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This is a really well known issue and I believe the fixes for it are some what private for the time being, however with that said I am aware that this is being looked at by the Unspeakable team, both long term fixes and short term.
Thank you for taking the time to create this suggestion! After discussion amongst the Leadership team, we have decided to decline it, unfortunately. While we understand the reasoning and concern behind this suggestion, we would rather keep Greenshore at its current level, as well as keeping the quest where it is. Instead, we will look into adding more quests to Antrum and Rushstone, as well as adding more high-levelled mobs to the mainland. Regardless of this, we hope that you continue to make more suggestions and share them with us in the future!