I feel the same as you did. Not long ago, I said that Zao needs a buff, and then Zao received 12km torps, this allows more game style, but this is not enough. The characteristics of IJN CAs, in my opinion, are heavy HE punches but long reloads, a decent torps, poor AA, and light armor in terms of CA class. These features allow IJN CAs to hunt DDs, burn down BBs while relatively poor against other CAs. But as more and more T10 ships with a variety of special consumables introduced to the game, if you look at Zao's specs, it's just not right and sufficient. On paper, Zao has great tools to finish her job, but we all know what really happens in TX games =).
I feel like Zao's poor HP and armor are still limiting her heavily. When hunting DDs, MSK, DM, and Minotaur have radars, Zao like Hindy needs to push into the cap to be effective, but Hindy with its armor can get way after finishing her job and she can heal more(+1 repair), while Zao with its low HP and poor armor will probably go back to port. So same logic applies to every other kind of fights again BB, CA, DD. Seriously, even an IJN DD can chew off half of your HP within the duration of one smoke. All this results in an incentive for Zao players to not to engage anyways but only kites away and run. How can a Zao be influential like this?
The solution in my point is simple, give Zao or other high tiers IJN CAs better heals. Not like the royal navy's crazy heals, but only slightly increased duration time or healing per second. In this way, they can stay engaged longer, and to be more active.