The reason it's not the same is that every shindigs I is the same. Their spirit just doesn't manifest itself all day. They still need their spirit to teach give them the power. Stark and lili are separate beings technically. Kenpachi and yachiru are not. She just manifested which makes her seem like a separate being but they are not. Which is why she just randomly disappeared when kenpachi used his true Shikai. Because she was always just a projection of his soul. Kenpachi didn't absorb her back into himself because she was always there.Not really as a manifested Zanpaktou spirit can still only be viewed by its wielder unless there are very special circumstances/very special material is used. Yachiru on the other hand is a physical being that can be perceived by anyone and has been living like a regular shinigami among them for a long time. This is exactly the same thing with Stark and Lilinette. If Stark wanted to use his full strength, Lilinette had to transform into his weapon. Now Yachiru gave Kenpachi his bankai, which means his strength was also separated. So on all aspects what Stark and Lili are is seems to be exactly the same as what Yadhiru and Kenpachi have.
Personally I'm still not entirely convinced that Yachiru herself is Kenpachi's zanpaktou spirit and that she might have been holding on to Kenpachi's power, but if she is, well then they're pretty much the same as Stark and Lili as his power was divided into two physical beings. You say that technically they are still the same, but you can say the exact same thing of Lili and Stark.
And Nimaiya is really not a correct reference as that's the guy who made Zanpaktou and who uses a Zanpaktou that has to be kept in a water tank. All those woman also were not wielded by anyone, so they should have looked like the Asuchi, but they didn't. So they really weren't normal.