Yeah they are without a doubt the BEST naval country by a large edge. Still all the rock-paper-scissors rules still apply, even if your scissors go blunt on his stone a bit faster. So that means:

- When he brings battleships, go subs and NB's;
- When he brings subs, bring 10CR-1DD stacks, or patrol with NB's;
- When he brings cruisers, go BS;
- When he brings NB's, try to catch them with interceptors and use cruisers to defend your stacks;

You will always suffer the tactical disadvantage because of his speed bonus, which is the most important in naval of the three branches. Basically you must outproduce him, but even then he can always run away from you and pick his fight at a different place where you are vulnerable, later on.

You can basically just say "best of luck!" to anyone fighting a Japanese navy in the hands of a capable player!

There is also the fact that if a Pan-Asian player is good and highly active, they could use their speed and view bonuses to attack you, then move out of range and wait for your attack, then attack again. An inactive player will be Tsushima'd by this, but if you're highly active you could do the same against Pan-Asian player (harder though). Either way it's a highly effective tactic.

To defeat a Pan-Asian naval force, focus on a well-balanced fleet composition. Prioritize naval bombers to exploit their bonus against ships, while deploying interceptors to establish air dominance. Capitalize on the aircraft carrier bonus for added versatility, and leverage battleships for firepower and resilience. Optimize view range to gain early awareness of enemy movements and utilize move speed bonuses for strategic maneuvering. A coordinated approach that maximizes these bonuses will provide a decisive edge in sea battles against the Pan-Asian navy.

Let's see...
Naval bombers ☑
Battleships ☑
Carrier bonus ☑
View range ☑
No, this isn't how to defeat a Pan-Asian naval strategy. Naval bombers are useful in Axis or Allied too, and some advice is broadly applicable, but for the rest this is how to PLAY a Pan-Asian naval strategy.

Only an AI (or an academic ) could state the obvious and pass it off as knowledge