The catch for these new weapons is pretty simple:

The monsters fought to obtain them or the materials to make them are the hardest things in the universe. They rage after roughly 20 minutes and they have too much HP to easily kill or almost kill before 20 minutes has passed.

Although, people have gotten results from enfeebling the Scorpion and using certain types of damage on the Matamata at certain times that indicate each fight may have a unique gimmick. The Jagil's 2000+ damage en-spells are currently so ridiculously ridiculous that there's probably some trick there as well.