The C. Viper thing isn't completely irrelevant. Her child just isn't in the games because the kid isn't fighting, but it's still very much apparent that she's a mom. Her win quotes indicate it, her ending and storyline indicate it, etc.
Like, people KNOW Viper is a mom. It's not hidden knowledge. It's very much in the open. She doesn't have a direct relationship shown on screen besides her endings because she's doing her job, but you can very much tell within the paperthin meat of SF4's story that she's torn between doing her duties and being with her child.
It'd be better if that relationship was more out in the open, definitely, but it's nice that Viper isn't fighting for some generic ass reason like "MY KID IS KIDNAPPED" or whatever. She's doing her job and would rather be home with her kid because she feels like she's missing out on quality family time.