I think you meant to link to this comic.
I don't think Magic can do "anything." Best analogy might be a mosquito or biting fly. A horse is a lot bigger and stronger than a biting fly, but they can't see them well enough and move fast enough to bite them, and they may not be able to swat the fly hard enough with their tail to kill it. They can't invent a tiny cannon capable of shooting down just that one fly, nor can they build a box and lure the fly inside -- they are limited in what they can do. But a lot of animals will deal with one persistent biting fly by rolling in mud, thus caking their skin and blocking not only that one individual insect but also all the other flies, mosqutoes, gnats, etc. in the area. The system change is going from bare furred flesh they can get to easily, to mud-caked skin the insects have a hard time finding a way to get through. I'm sure if enough critters stayed caked in mud long enough, so that it became the usual, then the insects would evolve ways to deal with the change; likewise, humans will eventually figure out how a new magic system works, but in the short term, they'll be at a severe disadvantage compared to now.