yep, i will fix it next July patch^^
please refer to : https://xerigart.itch.io/lentera/devlog/264124/lentera-version-030
which said:
Regarding to EXP distribution: From the previous build, Players was able to overgrinding which cause EXP and Level abusement by defeating a lot of mons. Regarding to this, EXP distribution is adjusted: - The Higher the level of the mons will give you higher EXP - But the lower of the mons level than your level, the lower the EXP (minimum 0 EXP)
It's a common system in RPG that the higher level you get, the lower exp you can gain from lower level mons
also:
Note: We will keep watching and making changes of stats attributes, skills, equipments, in order to keep the game from RPG side is balanced.