Are there usable NFT gaming tokens on bitcoin's network already? Is there an NFT marketplace? You didn't seem to link the article so these aren't things I'm able to quickly find, but I doubt both at the moment (the main nft gaming platforms are still in altcoins).
The answers are yes and yes. The first Bitcoin blockchain game was called
Spells of Genesis, launched in 2015. It used Counterparty tokens for gameplay and players could also earn tokens through completing certain aspects of the game. Some of them are now worth
serious bucks as collector's items. Bitcoins 10-minute blocktimes are an inherent drawback to using it for gaming but peeps have found ways around it through the years.
10 minutes is the download time of a small game imo. A 20GB game (for example from the early 2010s) could take from half and hour to an hour and still seem like a reasonable/good download time imo. If cryptos the same I don't think too many people would care (axie didn't mint your slp when you earned them, they were just staked until you hit the claim button - and that was on an native chain).