Too many excuses dodging the important question "Would type 93 MK1 torpedoes be overpowered?" The Answer is no, as only 2 IJN destroyers cant use them, and the earliest ship that can mount them is level 16.
The Tsukikei are the only IJN destroyer that cannot use Torpedoes. The rest of the IJN destroyers and most light cruisers can and are highly encouraged to use Japan's Secret Weapon, the Type 93 Long Lance torpedoes.
Type 93 torpedoes, unless used in huge waves from the Kitakami are quite reasonable, divided into low-damage/long range, high speed/short range, or low speed/high damage variants.
A DD1 that can mount 8 makes you complain, but a DD2 that carries 9 is OK? It would be a small change to the game, hence the title. There is little reason not to make this small game change. With weekly updates its no unreasonable to ask some ships be updated.