Yes there are many examples of soft g before i, like gist. But English orthography isn't self-consistent, so ultimately all these arguments become reductio ad absurdam.
G in GIF stands for Graphics. Period.
I agree that g for graphics isn't a terribly good argument one way or another. But the reductio ad absurdam part is the more important bit. All language, ultimately, is arbitrary, with successful information exchange being the only measure that really matters. It's especially so for something like GIF that occurs far more often in text than speech.
I find the "G stands for graphics" an extremely weak argument. In English the pronunciation of acronyms never seem to consider the pronunciation of the original words. Examples include scuba and laser. If you pronounced those like the letters in the original words, they would be pronounced scuhba and laseer.
That said, pronounce it how you want, I don't care. You don't need a reason to pronounce it one way or another beyond "this is the way I heard first" or "this is the way I hear the most". But the "graphics" reason is not a good one because (at least in English) nothing else follows that rule.
Probably like the peanut butter, because I wouldn't want it to be confused with my gorilla with the name spelled the same way, but pronounced with a hard 'g' sound.
If the only reason to pronounce it 'jif' is because of the context of it being a giraffe, then its a bad name and it also kinda proves the point of everyone who says that 'gif' shouldn't be pronounced 'jif'.