It's interesting to think about - because Big John obviously takes some time to connect/setup but then can (apparently) deliver 10,000 gallons per minute as long as there's water in the pipes.

Whereas a modern tanker truck can do 1,000 GPM for 2 or 3 minutes, but can do it immediately upon arriving onsite.

https://www.piercemfg.com/fire-trucks/tankers/bx-tanker

It's also relative to how fire-fighting has changed over time, modern buildings that are big enough to NEED the Big John are also much more fire-resistant (concrete instead of wood, etc).