A proper datacenter can be both efficient and safe. Add solid blidners to close the chimneys, and an oxygen suppressant system (NOVEC, etc.), and add motorized switch-fuses. They can all be orchestrated by a PLC, and a fire alarm/control system.
Close blinds, release NOVEC, disable power rails to computers. That's all. It might not stop everything, but it can help a lot.
You can even have passive gates to close ducting which have a wax element which releases if it gets too hot. No extra electrical or PLC knowledge required, just put these on your inlets and outlets and you're good to go.
Unless you assume other people's money is unlimited (which is the accepted industry standard for online discourse related to subjects such as safety and reliability) there will always be tradeoffs.
It's really easy to make low effort comments about the right balance being obvious when you're defining the right choice as "literally any balance of factors that does not recreate the precise set of circumstances that lead to the events that spurned this discussion."
Which providers were you looking at? IIRC Huawei was the only company providing ISO container DCs, but the were super low density (e.g. 50kW total) compared to what the original Google/Sun/HP designs were.
Close blinds, release NOVEC, disable power rails to computers. That's all. It might not stop everything, but it can help a lot.