I only recently made it into Pyros, so I can only really comment on Anemos and Pagos, but...

1) Quest locations, they're all in locations with enemies higher level than the quest needs. Make the quests more reasonable by placing them in areas where you can fight the enemies solo, using Pagos for example the level 23 quest makes you walk past level 27 enemies which will murder you horribly if they see you.

2) Mounts, just allow people to mount from the very beginning, locking mounts until you reach max level and finish the quests in the area just makes getting around more annoying.

3) No RNG grind, specially with something like light... Grinding for light to upgrade your weapon by itself isn't all that bad, but when you add a drop chance to it, it quickly becomes very annoying. FATEs and Dragons were the only way to realistically get any light in Pagos, and the dragons didn't always give it. Overall, if you want to do a light grind in something like Eureka, just make all enemies drop light so it's just a set amount of kills needed.