See:
https://www.firefighternation.com/lifestyle/new-fdny-super-p...
Your basic modern fire pump unit can pump 2,200 gallons per minute (if you can find a water source that'll give you that much) and it'd typically have a crew of 4-5 firefighters on board.
So you'd probably replace it with 4 regular fire trucks? Then you've got just as much pump capacity, plus you've got the flexibility to send the trucks to different places.
Note that, for what it's worth, fire pumps are generally rated for their capacity when drafting from a static water supply (think, pond, lake, river, etc). Basically all modern fire pumps can easily exceed their rated capacity by a pretty good margin when pumping from a pressurized source, but then you're back to your point of "do you have a source that can supply that?" Still, there are ways. In my firefighting days we had some hydrants in our district (the ones on the big 30" main that ran right down the middle of the county in particular) that could individually supply 2000gpm. And nothing says you are restricted to using one hydrant! There are also all sorts of complex water supply evolutions one can run, involving relay pumping with multiple engines, drafting and using hydrants, etc.
At the major Grenfell Tower fire, the water network could only supply ~4,320 litres per minute (1141 us gallons per minute) [1] despite firefighters asking the water suppliers to maximise the water supply.
And that fire was attended by seventy fire engines and two hundred and fifty firefighters, as they needed pretty much all the breathing apparatus in the city. So they had substantially more pump capacity than they had water available.
[1] https://www.insidehousing.co.uk/news/lfb-did-not-follow-even...