If you are asking for a game-theory answer, there are a few things to consider:
- How do we rate the usefulness of the magic at a given level?
This is mainly based on in-world opinion and depends not only on the actual power and usefulness of the magic but also on the alternatives and the situation. If a group of people see themselves outnumbered and low on resources, gaining more individual power will be much more appealing than gaining more strength even though there are machines that can be operated with ease anyway.
- How do we rate the damage of deviation?
Terrorists and soldiers on a suicide mission might consider turning in an overpowered, mindless monster a good thing, in those cases even the worst outcome is positive so go for it. If "rampaging monster" is meant metaphorically, even normal people might consider it a risk worth taking if they need to fight for their life, family or similar, if they can achieve their goal even if they deviate, it is like going to war knowing that you might die. In a civilised society where the majority of the population lives in cities with no external thread, turning into a monster and dying within a year might be as bad as it gets.
- How many mages are required to continue the magic system?
If magic comes from within and there is no specific knowledge required to use and level up magic, the magic will always be used by some people for one reason or another while if a level-up requires a ceremony including the help of several mages that have mastered the new level, the highest obtainable level will go down over the ages even if everything else aligns perfectly. The truth will be somewhere between these extreme examples.
- Who has a say in who levels up?
Is there a mages association that has to grant permission or help? Can a superior force someone to level up? Are level-ups an inevitable result of using the powers? No way to sort these questions out without knowing the specifics of your world and magic but they will affect the use of the magic. If using the magic results in level-ups, it might get discontinued altogether, if someone else than the user has a say, it will subject the issue to someone else's game-theory possibly with more concern for public safety or less concern for the user's life.
- What is the chance of deviation at a given point?
Chance of success times value of success minus chance of deviation times cost of deviation. If a deviation is the wanted or at least an acceptable outcome, this is redundant but otherwise, the result must be positive for an individual to risk it and considerably positive for a society to keep doing it without losing the knowledge due to natural fluctuations in the perception of risk and reward. If a deviation is a gam-over, there will be no content people who want to live a peaceful life and still use the magic unless the chances are extremely low.
Shadow of the Conqueror by Shad M. Brooks has a similar mechanic where one type of magic can only be obtained by conducting a ritual that has a one in three chance of killing you. On the other hand, you get powers that are orders of magnitude higher than anything a normal human can do and the other two kinds of magic can be forced upon you but are deviation 100% of the time or are granted, not obtained, after years of dedication. Even the characters do discuss that it is only worth risking your life in the ritual if you are either extremely power-hungry or there is a strong external thread that is worth risking everything to fight against.