Both of the changes are aimed to obsolete the original IJN destroyer line. I assume 30-40% decreased damage in randoms (mostly due to earlier death to radar ships) and by far the lowest winrate in ranked for them.
Why are they doing this? For the same reason as they removed stealth-fire, put extra caps in form of buffs to ranked battles, changed carrier focus to destroyer hunter and introduced IJN gun destroyers as replacement. Because they want to change the game from strategic to “mindless fun brawling” game. The stealth-torpedoes of destroyers are “not fun”, as the attacked ship has no way to retaliate. Sure, his teammates, especially gun destroyers and radar cruisers can hunt them down, but the attacked ship cannot. They probably recorded how many players ragequit over a torpedo devastating strike and decided that it should not happen. Sure, ships can and still be defeated by certain other ships, like a Yamato will win 99% against a Bismarck in random battle, but the loser ship can still make (quite ineffective) hits and actively play, while he cannot do the same against a Shimakaze.
The new plans seem to be redefining destroyers into escort light cruisers who travel close to bigger ships and shoot, relying on distance and evasions for survival, not concealment. Sure, a battleship has trouble hitting a Khabarovsk, but he can try, therefore feels he is not hopeless and blames luck when he misses.
I’m not sure what will I do after the de facto removal of torpedo destroyer play. Mostly it depends on aircraft carrier prevalence, because I liked the AA destroyer play. It’s a last hope, I have to add. However I do expect them to give a similar refund for IJN destroyers as they gave to carriers after the rework.
Update: I can’t believe that reddit agrees.
PS: it’s weird after a post like this, but: