90% agree, the CFTC doesn't consider these futures contracts, it regulates them under its "contract market" authority, that Congress designated and updated periodically over time

This is the authority on the CFTC's own website on prediction markets "For more information" section

https://www.cftc.gov/LearnandProtect/PredictionMarkets

https://uscode.house.gov/view.xhtml?hl=false&edition=prelim&...

And yes, both the Supremacy clause and the Interstate commerce clause neutralize any 10th amendment claim, unless the Federal government or any of its agencies was completely mum on the activity. But since the Federal government has exerted authority over that industry, via the interstate commerce clause, states can pound sand.