With a 2.1 sigma, however, those overpens will still be more likely to be uphits than misses, and even if all of the hitting shells are indeed overpens (which isn't guaranteed), the high Alpha can do a rather significant amount of damage even with overpens.
She isn't any more immune than Yamato, yes, but she isn't exactly anywhere less immune, too, considering the fact that it is a tier lower. Sure, much worse side armor, but either way with the high citadel it's going to be as likely to be cit by the guns of the tier. By lowering the reload to 30 seconds, you now have the unparalleled best bowtanker, because it's essentially the Yamato taken a tier lower and with the secondaries to screw anyone who wishes to come closer by the sides. Not to mention that the 60+% torpedo protection will be brutal for T7 destroyers and their torpedoes. Giving it better Maneuverability and a superheal is atrocious, especially considering how that is meant to counter CVs; you do so by sticking with your teammates and by not having a significant CV population. Comparing a balanced ship to the Arizona is flawed at best, considering the fact that it is currently the best performing T6 BB.
I don't see how giving more buffs to a ship that is already downgraded from T10 isn't going to make it OP.