Just off the top of my head, the way soul transfer seems to work is that a "mind" is basically put into a "body". Much like any normal human can control their own body, as per its limitations allow (for example, Zoro's skin doesn't stretch like Luffy's), it makes sense to me that a soul inhabiting an object would be able to control its "body", under its given limitations. The part of Nami's clima tact that changed shape seems to be made from rubber. If I had to make a comparison, it seems like the rubber version of wapo-metal in a way. In any case, it's not that unreasonable for Zeus to be able to change the clima tact's shape as the material itself was one that allowed for physical change in the first place.
So I don't think this is comparable to Napoleon, since he / she / it can alter the physical state of a hat into a sword. Personally, I think Napoleon's power is "fusion" and he's the one who makes big mom's fusion skills possible. But it's just a fun thought for now.
Umm...I think it needs to be pointed out that the Soul Homies are capable of logia/paramecia abilities because they are fueled directly by Big Mom's soul. She created Zues, Prometheus, Napoleon, and recently Hera by putting part of her soul in presumably a cloud, flame, hat, and cloud respectively.
IF we are going to not limit what one piece of soul can do...then Big Mom's ability is astronomically over powered. Each piece of her soul is multiple fruit abilities. Zeus is still in the form of a cloud despite him being only a "soul" (Big Mom is holding his physical "body"). We have already been shown what the pure soul energy is.
So what context implies that Zeus can create a club? Nami does not strike people with physical weapons. This is what Napoleon does.
I'm going to fight the urge to tag Weeby since she's mentally checked out, but it irritates the hell out of me to freakin overreact. Napoleon is clearly a he. Yamato is 50-50 on male or female. And nothing is "definitive" in ALL aspects until we get a decision from her AFTER Kaidou is defeated. If someone is freakin petty that a 50-50 decision not going their way stops the ability to be objective, then that is their problem. I feel like I know Weeby well enough that the "oh, poor baby" is not what she wants. Trying to be politically correct when Napoleon already has a clear, 100% male character is "oh, poor baby" to me.
One Piece is the worst series to be following for LBGT equality. Sanji, all the attractive females vs. eccentric females, Oda being the self-proclaimed biggest perv in the world, Kiku, and hell even the strongest potential flagship character in Yamato is best known for side boobs. Part of me wants the he aspect to become legit just to mess with the pervs, but declaring something as "official" when it is nothing but analysis is equally irritating. Hell, Oda doesn't even have much female equality. One Piece mothers are the literal sacrificial lambs.
As for the "fusions", that comes down to purely Big Mom to me. She was already to combine Zeus and Prometheus with her physical strikes (and I'm vaguely remembering both being used at the same time for something and this is outside of Napoleon plus Prometheus' flames). Napoleon has been shown in multiple weapons/blades. It doesn't have the same variability of Baby 5's ability, but it's what came to mind for me once we saw a second, third, etc. transformation of Napoleon. >
To be frank, I don't think Zeus or any other homie can be called Big Mom's power. The way I understand it, Big Mom simply gave part of her soul into things ranging from a simple bunny to an accumulation of a force of nature. In other words, she's simply using her soul as a "catalyst" of sorts in order to control a force that isn't hers. So in a way, Big Mom is borrowing power as well. So, technically speaking, Namu just got a hold of a force of nature that Big Mom simply gave a consciousness to and dominated. In other words, it's less that Nami got hold of part of Big Mom's power and more that one of the powers Big Mom was borrowing / controlling switched owners.
By the way, I certainly like that Zeus said he can't permanently leave the clima tact without Big Mom's powers. That implies that like all other homies, he's still subject to her power. Big Mom probably only needs to touch the clima tact to kick Zeus out of there. Hell, Nami will probably be weakened (in regards to Zeus) just by being near Big Mom. It was shown by King Baum that homies can't defy Big Mom's soul, even if it's a small piece contained in a part of her vivre card.
EDIT: Almost forgot. If ulti ends up being Nami's "official" opponent for this arc, that will be disappointing. It would be extremely anticlimactic for me, as Nami simply delivered the finishing blow, and it would not fit the power up she got.
Kk...this first part indicates further clarification of what differentiates Zeus, Prometheus, Napoleon, and Hera from ALL other Homies. "Homies" are anything Big Mom puts a soul into. Excluding the four names here, every Homie is made from the lifespan from Tontatta residents or lifespan Big Mom steals from enemies. The four named Homies are directly from a part of Big Mom's soul.
The first line just reeks of inaccuracy in all aspects. If Big Mom dies, every Homie dies with her (just realized that Big Mom being KO'ed by falling in the ocean is B.S. unless ALL the Homies have been undone; maybe if Big Mom created some with an awakening ability, this could be a potential bypass to keep Zeus, Prometheus, and Napoleon active. Either that or B.S. on how over powered abilities are negated by KO ). All Homies are directly from Big Mom's soul soul abilities. Zeus has logia abilities because he is made from Big Mom's soul directly. He requires to feed off of her physical energy (why she has to stay fat to fight for days) to perform attacks. This can be replaced only by the thunder-based weather eggs/attacks because of the logia ability.
Maybe the misconception is that we are not directly shown Big Mom creating Zeus and Prometheus? I think we've seen her create new Homies from the semi annual "soul tax" (or whatever the frequency was).
Because it is Big Mom's soul, that is the biggest B.S. It isn't some free to anyone power. It is purely Big Mom's power. Big Mom doesn't want to give it up because it is her soul and PART OF HER LIFESPAN.
The "cannot leave" the Clima Tact is because Zeus has been cut off from feeding off of Big Mom. I'm awaiting the raw to see Oda's word choice on this, but the mechanics have already been set.
It is B.S. And it's going downhill faster than I thought. Oda isn't going to have any tragedy based on the definitive breadcrumbs he's putting down now. These fights have become the climax fights and Oda has already contradicted the foundation of One Piece power ups for the crew. Big Mom has done essentially 100% of the work to defeat Ulti. Oda is indicating that Big Mom's powers will explain Nami's power up. Usopp, Brook, and Chopper might not get legitimate power ups.
The only remaining option are Numbers. However, these are all gag characters so far, so there's a cap on the meaningfulness of the climax fight.