It isn't really about cheating or godmode. It is about implementing situational spells.
Cleansing fire simply isn't as appealing if you have the opportunity of using it every 3 or 4 fights and even then you think about using it because... it is not better than throwing a fireball. Skills are supposed to be "balanced". Now you might say "hey cleansing fire should be stronger. that would be balanced".
Yes, you could make it stronger until people would start picking it, but this can be really contrived (like it now cleanses everything, which was not intended, and increases resistances because pyro should not have heals for reasons but it needs to do more because we cannot buff resistances by more than 30% and so on...). You might end up at a point where this spell is both so strong and so situational that it is more like a necessity; you need to take it for the rare occasions where you would be at heavy disadvantage without it and play the game with basically 1 skill less.
If you instead give unlimited skills to the player this problem disappears. You can either change the skill - the way you imagined - or change the specific encounter where it might be too useful. At the very least, you can leave it as is without doing much wrong.
Possibly the best example of competition victim might be Witchcraft: Resurrection. Why choose it/invest 5 points if scrolls are so fundamental and overly accessible?
