You realize you are actually arguing in favour of calling it like jiffy right? Because a direct reading of knife makes it kunifuh, and a direct reading of gif makes it the incorrect pronounciation as well.
Knife used to be pronounced k'nife. This slowly faded over time and is now completely eliminated.
By analog, jif being the original pronunciation is not important because the majority of people have decided to go with a hard G.
In other words, the "correct" spelling or pronunciation of words is democratic.