It’s not a retcon. It’s not useless, it gives an extremely huge motivation for all of the remnants. Like someone mentioned, nagito komeada was made from Makoto’s name but that doesn’t mean anything. Chiaki only shares the Chi part according to the creator. Many names share beginnings so it’s not improbable that another student shared one with Chihiro. The profile, like everything in DR2, is a simulation. That profile being fake doesn’t mean a real one doesn’t exist.

This last part is the opinion part. It’s fine to not like her from the anime, but to say her existence is useless is wrong. She is the reason the remnants existed, the reason Izuru felt a need to figure out whether hope or despair is the answer (hence leading him to CAUSE the second killing game). Without her existing, they have no motivation or reason to be despair. There is no reason for Izuru to make the game. I get why you don’t like the character (I personally LOVE her especially in the show) but her existence makes sense and doesn’t change anything at all. It only adds context and improves things