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The rewards like artifacts are even more reasons as to why no one likes PVP. Most people grind and grind seals just to get these artifacts to use in PVE; it's a chore that makes PVP even more despised as opposed to making it more enjoyable.
Ancient Lakoria's tail spikes and it burrowing underground are independent of each other. As Vladino said, Ancient Lakoria will sometimes attack again before burrowing.
Prior to the Rise! update I would have suggested staying on the opposite side of Lakoria (keeping it between you and the rest of your group) so that you can use your flinching abilities without upsetting too many people. Usually interrupting his tail-spikes saves lives, but there's little point since potion animations have been removed. If you're competitive, you can intentionally disrupt Lakoria to reduce the damage being dealt from your rivals because West is currently so competitive over the extra evil core rewards that I don't even want to participate in Royal Army.