Fire Magic is very weak against Slimes, it only does about 10% damage. They are also Immune to Lighting Magic. The reason it feels like the Magic Wisp does a lot is because they have no resistance to "Pure Magic" damage and have rather low HP pools. I will probably boost their Resilience (magic resist) a bit to compensate for it.
In general, it is probably not worth restarting every update as they usually only add one or two recipes which you might not even have any interest in.
I'll see if the "recipe book" approach would work, maybe if I make the Game Update event relearn the recipe it might work... I'll need to test this.