I think the implication that we're supposed to get from the original anime is that Chibi Chibi took the form closest to the person who she thought would be able to save the galaxy from Sailor Galaxia. She mentions in Episode 200 that she was looking for someone who could accept her.
But what gets missed is that Chibi Chibi's appearance is meant to evoke Chibi Usa more-so than Usagi because her whole point in the manga is meant to be one big red-herring. Because of the precedent of time travel, both the characters and the audience easily buy into the idea that Chibi Chibi is another daughter from the future (or even a granddaughter). In reality, Chibi Chibi was a delibrate disguise chosen by Sailor Cosmos so that she could easily get closer to Usagi without risking suspicion in an arc where all of the bad guys are Sailor Guardians. Naoko actually does a decent job foreshadowing this multiple times when Chibi Chibi slips up, whether it be displaying the full extent of her powers or suddenly speaking full sentences, it gradually becomes apparent that she is more than what she lets on (we even see Cosmos' symbol when she transports Sailor Chibi Moon and the others to the center of the galaxy). Disgusing herself as a Chibi-Usa expy also allowed her to comfort Usagi as she goes through trauma, so it even adds a more tragic element.
In the original anime, yes, she gets mistaken as being another kid from the future, but it's not made clear whether the light of hope intentionally chose to disguise herself as this since there's no reason why she would know who Chibi Usa is. So it reads more like a coincidence and starts feeling pretty contrived. Does she speak in mostly baby speak because she hasn't awakened yet or because she's hiding her true identity? I just feel like there's a little less nuance with her character in the original anime.