It's only 8:00 pm here so I'm still up.
There are lots of 4 door sedans that are brutally fast and handle great. Doesn't make them sports cars. Same with GTs. Nothing wrong with a GT, some of the greatest cars ever built were GTs.
The Genesis starts somewhere around $25k with a 4 cyl turbo. Swapping in a V6 would only increase the cost by a grand or so. The reason it costs so much is extra luxury frills and where they chose to price it. In short they know people will pay more for a bigger engine so they charge more.