Well, the problem is the lack of context under which his use of disaster would make sense. King has a remarkably complicated skillset all in all, perhaps the most complex among the sins. This is what we know for a fact so far:
Chastiefol is forged from the sacred tree. It has multiple forms, each of which seems to reflect aspects of the tree. King has mentioned how a form is the flower of the tree, the pollen of the tree, the mold of the tree and a number of other things.....
Disaster is king's unique ability. The only time we know for a fact it has been used was against cain whose rheumatism was triggered a bit. Other than that we have been told that disaster is able to draw out the qualities of the sacred tree.
Now, what exactly is going on here? If we consider what we saw with cain then it would seem like whatever disaster is used on should have bad stuff happen to it. So... wouldn't king using disaster on the tree directly kinda hurt it? We also don't see stuff like what happened to cain when things get hit by kings attack. Sure, people get hurt but its not like we see further bad stuff happening. Also, if we consider form 8

ollen garden it seems to be doing precisely the opposite of what disaster should be doing. How can disaster come into play there? I could buy disaster having something to do or otherwise enhancing the forms however to an extent it would be weird because the forms seem to be related to stuff the tree itself can already do and at least one form seems to be the opposite of disaster. Also, if disaster is needed to make the forms it would kinda defeat the purpose of having a weaponized version of the sacred tree. Wouldn't he be able to do the same without chastiefol? And of course, there is the possibility that king is using his disaster on some forms but not in others which would further add to the confusion.
Helbram had the abilities of a number of knights which he could have exploited and yet he never really added anything to his attacks with the tree. That always seemed weird to me...