AP is good against any cruisers that give you a broadside though. Even against broadside BBs they can do some decent damage.
tho the max range for Yamato secondaries is around 10km or so, any cruiser give you broadside in that range is dead long ago and you won't even bother to count on the secondaries to kill them.
In fact, almost 95% of player at that tier will surely angle agaist you and go for point blank torp or ram. those 155 have super hard time to do damage.
I just had a game which i end up in 8km fight with a bismarck, my 127 did 5k alpha damage + 2 fires set and my 155 did 0 damage against him.