Although the Landfall questline can be acquired by a level 20 character in Pandaria Remix, there are many level-scaling problems in that questline.
The most significant one occurs in the quest named ‘The Divine Bell’. I could manage level 25 mobs with level 20 characters, but I couldn’t interact with the final object of the quest - the divine bell itself. So I couldn’t complete the quest.
I wonder does this makes sense since the quest is still acceptable at level 20. I think this happens due to zone level(Kun-Lai for lvl 25, Valley of the Eternal Blossom for lvl 40), therefore the quest mobs and objects need level scaling for 20. Especially for ‘The Divine Bell’ which cannot be completed because of interaction requirements.