Though dungeon skill books and normal skill books had the same purpose of giving one a skill, the strength of the skill contained in each one was akin to putting a tennis ball beside a basketball. Similar to how there existed various tiers of equipment, tiers of skill books also existed, with the ones most sought after only being obtainable from world raids.
After that were those that came from reoccurring field events, then those that came from dungeons, and at the bottom of the barrel were skill books that could be bought from shops. As for skill books obtained from auctions, though the quality of the skill in it generally varied, the worst one could obtain was a dungeon skill book.
Considering how dungeon skill books only became a common drop in dungeons made for Rank 5 class holders, it was no surprise that Valyr felt a great amount of excitement at being able to obtain a dungeon skill book this early on.