SinfuLeeCerebral it's exactly as you have said it. The rune break on it's own has the capacity to destroy the seals. But a seal of that magnitude, which is made of a combination of rune sentences, with each individual word powerful enough to affect nature. It will take a significant amount of power both mental and soul for Kael to break that seal.
Remember I also wrote about individual runes that are tailored to a weaver. Break is one such rune, but it's true power can only be showcased if Kael can get to a higher circle or a higher realm. He doe's not need to be as strong as the person who weaved the seal to break it. He just needs to know where to hit, and hit hard. I can't say much unless you want it spoiled.