There are many synthesis recipes according to the lodestone, which need multiple treatises but the in-game "Recommended Skills" never shows more then one. Recipes given from local levequests lack important information like sub craft rank requirements or recommended treatises so it should at least show all the recommended books in the synthesis starting menu. I do miss the how recipes in Final Fantasy XI were available for easy viewing at their respective guilds with complete data on things like necessary key items. Perhaps there can be a NPC to store all the learned recipes of a player to view in game.

As for the ****kin Eluder type skills, I have purchased and played with the few and although they do work properly, they are incredibly hard to use. They are single enemy targeting skills with a 10 minute reuse timer that lasts only for 30 seconds. They are usable only while playing as a Disciple of Hand or Disciple of Land class and changing classes would reset the reuse timer to 10 minutes. (This includes any class change, even between two appropriate classes; weaver to carpenter, etc.) The range of the skills are very short as well with monsters who detect by sound possibly becoming aggressive before being able to use the skill. With scattered monster placement and often wide areas to move through, the skills are worthless considering each costs 8000 guild marks. The skills need a complete reworking if developers ever wish to make the world of Eorzea more dangerous. There is just no situation where I would need to pass only one aggressive monster safely and be possibly willing to wait 10 minutes to do so.

My recommendations would be:
1) Self targeting, 1 minute duration of aggression invincibility towards all monsters of the Eluder type.
2) A reuse timer of 3 minutes.
3) The removal of resetting reuse timers upon class changes.