The tokenomics are important. They could create as many PoW blockchains as they wanted without the coins being securities. The important part is that they created all tokens themselves and then sold them via ICO with funding rounds to investors who expected to make a profit from it.

https://www.coingecko.com/en/coins/ftx-token/tokenomics

I think it is more of a stretch to call FTT a cryptocurrency than calling it a security.