There is also this nice analysis in another topic
I think many if not most of the A rank are actually underwhelming, since many of them are worse than B ranks ...Also, Jeralt Mercenaries are E-rank (3 atk, 10 crit, 15 avoid) and still great, even in the endgame for people with deficiencies in authority (it fits Felix as a swordmaster/assassin super well)