The game loop of Rose is about leveling a character to the main level and farming until one has their gear fully maxed out.
It would be a strange user experience, if the game enforces users who worked months towards the goal of maxing out a character are not able to farm the materials they want with the said character. From a UX perspective it would be difficult to explain to a user, that they worked month towards maxing out a character, just to notice that they are not able to farm the items they want to farm and start all over again.
Since certain valuable items can only be farmed by killing specific monsters, those monsters also need to drop items for maxed out players.
Something to consider, item catagories that can be farmed in every level range, e.g. chems, catalysts, ..., should not drop for players outside of the level range of the monsters.
E.g. It's ridiculous that maxed out players can farm chems in the goblin cave, while Armastyx are also dropping chems.