I'm sorry but you're dead wrong about the BMS. BMS doesn't address any of the things I listed.

You're also wrong about standardization - standarization at the cell form factor level is correct. Different applications have different capacity vs power density requirements, temperature range requirements, cost, lifecycle... a pouch cell that goes in a drone looks a lot like one that goes in a cell phone but they're optimized for completely different workloads.

Also we already have standardized interfaces for external batteries with most power banks using USB-C, so in a way your wish has already come true.

Went and found the LTT video. It's unclear what he did there. He said there was a spark, and then he ran outside with his pack. Spot welding the cells isn't usually that fraught.

Yeah burying a thing in sand is legit. Depending on the size of the thing that's on fire, water might be fine. Standard protocol for electronics that catch fire on a plane is to apply water to cool the device and extinguish materials around it, and then to put it in a special fireproof bag with a bunch of water.