If magic attack bonus affects quick draw, I don't think it takes much of a leap to think that magic accuracy also does.
As for the agi earrings, like someone mentioned, increasing your fstr is better even for slugshot, and if I remember correctly ranged fstr is calculated differently (I believe it rises quicker?).
My feeling about the stats on that weapon was basically the same, but I admit that it's a shaky argument to claim that the m.acc on that gun doesn't "seem" the same as, say, looking at INT on Rogue's Bonnet and saying that INT must affect steal. One could just as easily say that the m.acc and MAB were mirroring the negative r.acc and r.atk. I will say that, aside from a few with random elemental resistances, guns don't tend to have stupid random stats. I mean, well, look at them:
Marksmanship - FFXIclopedia, the Final Fantasy XI wiki - Characters, items, jobs, and more
Those two gun+earring pair guns have a few oddball stats, but that's about it. Not that SE doesn't still have a fetish for adding totally useless/WTF equipment.
No one within the last few posts contends with the idea that Magic ACC affects Quickdraw. It's simply a debate about whether gear stats are plausible grounds for believing that a particular stat affects some aspect of some class. That said, I present Narval and Roundel Earring! Obviously works on our Healing Breath! Right?!
That was never a debate either. Maybe it is moreso now than it used to be, but I think everyone is fully aware that SE has put some completely off the wall stats.
The debate is how MUCH Magic Accuracy helps. Much like pretty much every other Magic Accuracy related question, nobody really knows for sure. I'm going for the AGI earrings over the MAB ones because...well, I already have one of the AGI ones, and it's better for ranged attacks, an area where my stats are lacking.
If someone wants to go out and test 10,000 Quick Draw attempts with AGI vs. Magic Accuracy, please do. But until someone does, it's a silly argument because nobody really knows the answer.