Sorry am I understanding you’re going to keep level 80-120 mobs on Agnarr when max character level is 65 ?
Nah, you are not understanding. The 80+ mobs will be tied to Veil of Alaris expansion which will never launch on Agnarr.
Correct, they don't give xp. They spawn super fast and are very easy for their level. They're just for the quest.
But the scaling is not very well done. Spells used by the mobs are very over powered at level 65 on Oakwynd and some of the spells have little to no scaling between levels. Some of the spells are effectively an AoE deathtouch, hitting everything in the room for 23K plus in an era when raid geared tanks only have 1/2 that number of HP.