There's a lot to say about the phonotactics of English and how weird it can seem. C and K are both necessary, consider the word "Ketchup." Are you going to call it "Cetchup" as a replacement? That doesn't look right. "Kill" wouldn't become "Cill," either. Your cities would become kitties in the blink of a tongue.
So, the real question is: *Why do we keep C?*
The answer is pretty simple. Besides keeping etymological integrity, "C" is a part of an important duo that creates a rather unique sound. Our affricate king /tʃ/. As in "katch." Actually, funny enough, English loaned this specific spelling of the sound from France. Originally, it was just <c> doing all the work on its own ("ic" instead of "ich," or "benc" instead of "bench"). We can't really replicate C's success in English. But C would be awful on its own unless you'd like to open up an entire salami salad of new exceptions in English.
(this Smogon post was brought to you by 100 monkeys furiously pounding at their keyboards)