You underestimate how much rng can screw a person over even when stacking the odds in your favour. I have the the high end BiS pentamelds and HQ food, and even with using the correct skills at the right times I can't get lucky enough with the gatherer's boon ones to consistently achieve Gold ranks.
And then there's absolute bullshit like that one Class A ALC mission that asks for three crafts each requiring you catch a specific fish that is the rarest in a pool of five and can't be helped with Identical Cast or Double/Triple Catch, all on a strict time limit. I've attempted that mission over a dozen times and I've only twice actually ever caught one of the necessary fish, and both times it was with barely enough time left for the single craft that it enabled.
Upgrading the relics require Class A missions due to the IV's.