It’s not really much of a problem, here’s why.
First off, it would cost precious TP to reset. Why spend on something which you can attain for free when you can buy something more useful like Tokens, costumes, etc?
Second, early game leveling is made trivial by the existence of Pardoners. Simply buy buffs, get an Arde dagger (which you can get in less than a day through farming/hunting items) and proceed to wreck everything in sight with auto attacks. Now we weigh in the initial idea that resets cost TP. So, you have the choice of using a small amount of in-game silver to buy buffs, or choose to spend a huge amount of TP just to reset your character’s classes. What’s the most practical route to choose, for you?
Third, even if a user is unfazed by the idea of an expensive TP item, or the actual ease of early game leveling through Pardoners, then I say let them spend that TP to change their class. The person will waste their money, IMC will gain profit, and everyone else will stay uncaring about whether or not the person just changed their class or not, because in the end it will be no different than a person with the same build who never used a class reset.