I honestly do not see a nerf to BB's. I only see it as a nerf to specific BBs, mainly the USN and IJN lines . At high tiers (T8+), The RN BB line still has its HE shells that is rewarded by large damage and fire chance and both the French and German BB line are secondary capable. Furthermore, the Republic isn't exactly lacking in long range accuracy and hydro is a thing for the GK. People say adapt and overcome, and yes, if the changes do go through people will adapt, just not necessarily in the way we might think. I think we would see less Yamatos and Montanas and more Conquerors, GKs and Republics at T10. Some have been arguing that long range pot shots do too much damage on a ship that cannot heal, and while I do agree, I think that every ship is in the same situation (but they, unlike most DD's do have a heal).
On mid and lower tiers, I can see where this might help DD's as some lines cannot stealth torp and gunboating can be difficult. But is BB AP the true reason for this issue or is it a part of a much larger problem? Is it even a problem? Honestly, I cannot state an opinion on that in full confidence, but I do have some thoughts...
Maybe instead of hard nerfing BB AP on DD's we look into buffs for DD's. Torpedo range and speed, torpedo spotting range, torpedo reload timers, smoke duration and DD HP can easily be tweaked on a ship by ship basis compared to blanket nerfs which seems well intended but ill conceived.
Finally, I would like to argue and stress the importance of fixing the double-dip bug in a timely manner. I think that looking into BB AP reduction values on DD's across the board seems illogical when the viable of double dip is still around in addition to my above arguments.