You're linking an article showing how everybody in modern times who uses the term "uniparty" is using it to further their own political interests...

Beyond just that, if there is a uniparty, then why is Elon spending half a billion dollars in electoral races?

It's not that there's a uniparty, it's that as a result of Citizen's United, parties don't need to represent you anymore. They represent their money donors instead. Money is speech now, and as the wealth disparity grows it becomes a bigger megaphone and drowns out the voices of hundreds of millions.