#2 (crypto transactions backed by traditional currency) is far and away the most useful of these categories.

Unfortunately, it doesn't offer the speculative upside of something like Bitcoin. People don't actually care if their transactions are carried across a blockchain or a database, as long as it gets done.

Bitcoin is hot specifically because it's so detached from any real-world use cases or metrics that might put bounds on its price. There's a narrative that because no one can determine an upper limit for Bitcoin price, there's infinite upside. Of course that narrative is no different than any other arbitrary asset, but the Bitcoin narrative is strong because it's been in the news so much.