Vaan had to admit he had slightly underestimated the potency of the Divine-rank Stalactite Milk. But if he hadn't, he might not have discovered a special method for tempering his channels.
The biggest difference was brought by the increased 30% effectiveness from his Earth Spirit Body, which he did not anticipate.
After all, the system already allowed him to absorb 100% efficacy of any consumable product with medicinal properties. It was normal to assume there was nothing left to absorb beyond that.
However, the reality of the situation was quite different. He ended up absorbing 130% of the Divine-rank Stalactite Milk's potency. That was why it felt so overpowering.
Nevertheless, that just proved Vaan still knew very little about the divine rank.
Despite all that, Vaan was fortunate to make the mistake. He had gained a lot of it. Even so, he still hoped he wouldn't make another mistake. The next time might not be as unforgiving.