Given that a typical lithium vehicle battery back only contains precisely 0 (ZERO) kg of the metal[*], I suspect you have not the first idea about the chemestry of Li-ion-battery fires.
That first idea would be that a Li-ion-battery contains a number of different and unusual chemical substances that make up the negative electrode, the positive electrode, the electrolyte and other components, that these react in complex enough ways while the battery works as designed, and may react in many more complex and sometime poorly understood ways when the battery is subject to abuse and outside its operational envelop.
So that first idea should have tought you that the mere numberof kg of Li in a battery does not tell you much.
Also, these batteries are hazardous not because of their size and total stored/released energy, but because of peak temperatures and the difficulty/impossibility of suppressing the initial fire. So your point is pretty irrelevant.
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[*] When a Li-ion-battery already malfunctions or operates well outsides its envelop, it may deposite a layer of elemental lithium on an electrode, and that constitutes a hazard, but the amount of such elemental Li will remain very low, a very very small percentage of the total Li