In this case, the fire was an accident, and the arsonists happen to be the expert firefighters, and they're very motivated to fix their mistake. They're still the experts in all stuff fire, whereas Delta is not.
Using your analogy - if MS/CS are the arsonists, then Delta are the landlords unsafely storing ammonium nitrate in their own warehouse.
Their lack of response to MS/CS isn't coming from a place of reducing potential additional problems but trying to shield their own inadequacies while a potential lawsuit is brewing in the background.
It doesn't seem like arsonist is the right word. It implies it was intentional, which as far as I can tell there is no proof of.
I think the more accurate description would be some firefighters were doing a controlled burn. The burn got out of controlled and then you say that you don't want
the firefighters help in put out the fire.
I’d reserve judgement. Delta may have been cautious about giving the arsonists a wider remit.