Sales numbers aren't really all it's about
Sega existing was more proof of concept that the space was big enough for multiple entities. I would say they are what helped make multiplatform development a standardized thing.
Microsoft meanwhile paved the way for what is now standard modern online practices with how it implemented its storefronts and Xbox live.
I do think Atari is in the discussion for third here but I personally have it as 5th and don't think that should be as much of a hot take as it apparently is.
No problem!
This is a cute and pop genocide of love!