I'm not a game developer, and know almost nothing about the process.
However.
I'm pretty sure switching to a whole new engine (UE4) means Project Soul can't simply "copy and paste" from previous titles.
I don't like using the term "copy and paste" as it's never that simple, but they can still reuse almost all assets after switching to a new engine. If they're able to reuse the same animation skeletons as previous SC games (which I think they are since the animations seem to be deforming the meshes the exact same way) then they can reuse all animations, meshes, rigs, and textures if they want. They'd need to convert all of that stuff but UE4 comes with tools to convert from standard formats so I don't think that step would be a big challenge.
I don't want to downplay Namco's efforts too much. Using a new engine definitely comes with a lot of unique challenges. The only thing which makes me think "Really?" is the hair, everything else I think looks fine. But I'm really baffled they're re-using hair models which were designed to be rendered with a smooth alpha.
Im pretty sure ALL the character models are new. Just look at the faces. The hair is too. Campare them side by side if need be (with the highest quality resolution u can find). And ever since 2 Ive thought SC had some if THE best voice acting in any fighter.
Cass in SCII particularly but also III, Seigfried and Maxi are also very fun to quote.
(Especially that "Goddamn Freak" line from SCV lol)
Ive honestly NEVER heard anyone bitch about SCs voices.
I've been comparing characters to previous games as they're revealed and there's usually some pretty blatant asset reuse. Some quick examples...
Ivy's hair mesh and texture look the same:

Ivy's weapon looks to be using the same mesh and texture:

Zasalamel looks to be using the same face mesh (though tweaked a little). The little you see of his weapon looks to be the same mesh:

But for the most part, I think that's fine. If they decided to reuse some assets to save time and spend more time making new assets, then I'm completely fine with it. Especially with CAS I think it makes perfect sense to reuse assets as that lets them start off with a similar quantity of customization items as SC5 and then they can add to that.
The only thing I wish they would have done differently is the hair. They're not even trying to hide how bad it looks in official screenshots:
