All the debuffs are subject to diminishing returns over the course of the fight. For monsters with only 1 star weakness to Blast, technically poison is probably going to be a better option then blast in terms of absolute damage over the course of a fight, but poison won't cause a stagger like blast can.
All the debuff effects (including KO) follow the same rules, the monster has a hidden value where once the applied status crosses that threshold, the debuff is applied. Once said debuff has been applied, the value needed to reapply it goes up.
For weapons that have a really big single hit (so basically GS and Hammer), Sleep is likely a better option then blast because it will overall lead to higher damage output, and the sleep can also lead to a free wall bang since putting a monster to sleep resets Agitator.
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