Two points (ok, three):
1. 2 triple 12.75-inch torpedo mounts are the standard ASW outfit for USN (and RAN, etc) ships... they launch the Mk 50 anti-submarine homing torpedo.
2. 13,500 tons (18,00 tons full load) is indeed the same size as Principe de Asturias (17,200 t. full); almost the size of Invincible (20,600 t. full); and a fair bit larger than Giuseppi Girabaldi (13,400 t. full)... if it didn't have all of that ASW/AAW and Command-ship gear eating into volume that the afore-mentioned ships use for stores and aircraft hangars.
The 16DDH ships will not be nearly as capable as either of the first two as a VSTOL carrier... the best match (air capability-wise) would be Girabaldi... the extra tonnage seems to be used for the AAW & Command facilities.
3. The Japanese Constitution says NOTHING about any type of ship or weapon...
"[CHAPTER II. RENUNCIATION OF WAR] Article 9.
1. Aspiring sincerely to an international peace based on justice and order, the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes.
2. In order to accomplish the aim of the preceding paragraph, land, sea, and air forces, as well as other war potential, will never be maintained. The right of belligerency of the state will not be recognized."
If you take an extremely strict reading of this, then the entire existing "Japanese Self-Defense Force" is unconstitutional, period. Japan does not have the right to conduct war for any reason... even Self-Defense!
Lesser readings allow for all sorts of equipment and forces for "Self-Defense", but none at all for Offensive war.
In that context, flying Dave from the 16DDH class would really stretch the Self-Defense claim... while flying ASW helos is perfectly allowable.