Not at all no. Rachel is literally a completely different character. they don't even have similar play styles.
For the millionth time, I'm going to break this down. And this will be the last time. And anyone dense enough still not to understand this concept is an intellectual failure.
There are two aspects of this: character and gameplay.
Character: Yes, Racel's a different character from Nicole. Nyo is also a different character from Bankotsubo. They share some similarities, such as being ridiculous and saying some nonsensical things. Rachel and Spartan share similarities as well, such as being rather arrogant and confident in their abilities and demonstrating a clear superiority complex with a clear sense of duty and loyalty to their mission. Not the same, but having shared elements in terms of the general idea (DOA2 Ryu and DOA5 Ryu personality-wise are arguably more different than Rachel and Spartan are to one another, but that's an issue for a different day).
Gameplay: Rachel and Nicole share many similar moves. Not all, but many. How these come together and function to contribute to the character's gameplan is notably different, yes. But this difference is no more severe than same-character iterations. Hayabusa functions far differently in 5U than he did in DOA3. He gained some moves, lost some moves, and also shares many similar ones through both games. But how these come together and function to contribute to the character's gameplan, once again, is notably different. So to say that gameplay-wise you need Spartan back would be to say that you
need DOA3 Ryu back. And no one makes that argument because they realize that modern Ryu is an imperfect
evolution of DOA3 Ryu, gaining and losing some things. This is similar to how Nyo is an imperfect
evolution of Bankotsubo and Rachel is an imperfect
evolution of Spartan.
So, the gameplay argument is stupid and anyone still making that is horribly lost. At best you're looking at a "I need my guest character's
personality back," argument, which is notable for a few reasons:
1) Nicole's personality was so one-dimensional it's hard to map without using a ruler.
2) Rachel embodies enough of the general idea to have a comparable evolution in this regard as Nyo to Banko, and is a hell of a lot more similar to Nicole in this sense than
P4 is to
Kasumi Alpha.
So when you say: "I like discussing what she could be like if they revamped her into a 'new' character like they did with
phase 4, Nyo and raidou lol."
and I say: "They already did," there is no absolutely no possible way you can rhetorically argue back and retain any semblance of a point that doesn't contradict what you had just stated moments prior.
On the topic of the new character: "biggest" could mean biggest breasts or biggest height or biggest weight. Any of them could be notable or completely un-noteworthy depending on the degree by which she's "bigger" in the respective element than the runner-up. It's not much to go by and hardly something I'd be focusing on.