"Young Lord, Rune Seeds are constructs of Mystic Intent, Mystic Essence, and Mana. You can liken them to a uniquely defined Intent Seed." Wu Yu began to explain to the best of his abilities. This was further enhanced by his recent insights gained from reading the Blood Origin Method. Moreover, Wei Wuyin realized that Mystic Rune Seeds weren't restricted to the Mystic Dao, but a topic of the peak Mortal Dao. Thus, unlike the normally obscure explanation, this one was reinforced by the full knowledge of someone who transcended Mortal Limits.
This startled Wei Wuyin for a moment, but his mind strongly stirred with excitement and elation. For the Mystic Rune Seeds to be at the precipice of the Mortal Dao meant it was comprehensible at the Astral Core Realm. This likely suggested that the explanation given wouldn't be incomplete by the trend of the ignorant and profound.
As conversations do, we go off-topic sometimes. Lol. That said, Utmost Purity Mist is never forgotten! Moreover, we have an explanation why there's such a difference in refinement time.
While not explicitly stated yet, I'll say this is why Kratos, Ori, Eden, and King has insidiously low refinement times. They eliminate the body and their own resistance from the equation. Sentient Spirits OP.