And if they did make this change, you/some other poster would ask for another bonus. Then another, and another, and another.
The XP buff/legacy loot changes ahead of Shadowlands are plenty nice as it is.
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I killed Mythic Jaina before EP/8.2 came out, didn't win the mount, and my group didn't kill her enough additional times for the whole group to get one.
So maybe come up with a less stupid/assumptive argument.