In defence of soft magic systems in literature:

Magic refers to the sense of mysticism that we feel in the world, the idea that we cannot explain everything in rational terms.

Truth is, we do not experience the world as a set of causes and effects, as clear, independent mechanisms acting according to their rules: we experience it as a whole event where some things have more meaning to them than they logically should, and this feels magical.

Having hard rules for magic deprives magic from its essence.