I don't think too many conclusions should be drawn yet from my 20 something games sample size. (Though amazingly, my winrate went down to 30% now 
)
Fair enough.
I didn't find Hatsuharu did very well as a ninja DD, so I played her as a fleet destroyer, and with bucky's higher detection range I was kind of forced to play similar to that.
Hatsu is very definitely NOT a good Ninja, especially since she often goes against the super-stealth Mutsukis. Anything can out-spot you at that tier. Hatsu needs to be played as a fleet destroyer / gunship (!) early on in the game, until the enemy DDs are cleared and
then switch to ninja.
Even so, I don't think I quite agree Fubuki should be played as a ganker, or at least, I don't think thats how I'll ever play her. Something like a Benson with 10x9km torpedoes and mean guns seems far more suited for that to me. What I feel makes Bucky mostly a poor ganker is her slowness. 35kts 
I've already been in two-three situations where I was going to have alone time with an enemy carrier, just for them to outrun me and kill me with bomber rng. Which made me feel very sad.
Fair enough - but it's all circumstantial. The Benson can engage from a distance (even stealthtorp, now) and cause huge damage but she's mostly dependent on guns / fires. Her torps are slow and do less damage than Bucky's - and if you engage with guns before the torps hit, the enemy knows there's a DD around.
Take everything I write with a grain of salt, because I haven't played her in a while:
Bucky is meant to stop pushes -
not push back (because, as you pointed out, she's slow as molasses). You make a swooping run across the front of the enemy advance and see whether you can spot enemy DDs (Bucky is the stealthies thing at her tier) and then a) spot for your cruisers, if enemy DDs are present or b) pick an enemy BB and close to ~6.5 km and launch everything. If all goes well, you've eliminated ~50% of BB firepower in that flank and made the rest very very jumpy. What she's got for her is that huge Alpha of the original torpstrike.
Then you pop an offensive smoke and start raining down fire. She's got good guns - 7% fire chance and +300 HE damage compared to the Benson. DPM is less, but shells are less affected by BB armour, so it evens out. Launch torps as you see fit during that time.
The moment the enemy starts retreating, that's it - you immediately break off and relocate to another cap point. You've done your job. You are not supposed to follow / harry them - that's for the CAs and the BBs in your team.
