A free mod for Witcher 3, by Atheosis.
Oils Rebalanced is a simple and intuitive mod that rebalances the game without changing the game's feel or gameplay. It's one of the most balanced and intuitive mods I've seen in a long time.
This mod removes the exponential increase in damage for higher levels. This means that higher levels do less damage than lower levels. This change was made to address the issue of high-level play being ridiculously easy while not changing how the game feels or how it plays.
The most significant change is that higher-level oils are less likely to run out during a fight. This is because the amount of time spent charging up an oil is proportional to the level of the oil. So, if you spend more time charging up more powerful oils, you're less likely to run out of charges during a fight.