It's the largest non-government-issued currency in the world, and its money supply exceeds that of many fiat currencies[0]. But since "massive failure" is a subjective judgment, it's hard to argue with that.
No, it's the largest non-government-issued speculative asset. A currency can support far more than 7 transactions per second globally.
Late edit: If I wanted to use a centralized payment network, I'd just use euros. The centralized euro payment network is much better than the centralized bitcoin payment network.
Bitcoin can handle just as many transactions per second as fiat currencies when used over the same centralized payment networks (e.g., credit cards, PayPal, bank transfers). The key difference is that Bitcoin also provides a permissionless, decentralized settlement layer - something fiat currencies fundamentally lack. If you're comparing base layers directly, it's arguably 7 TPS (Bitcoin) vs. 0 TPS (fiat).