If I understand your description correctly (and it is the way it should be done, whether jumpstarting with external battery dolly or using another vehicle), you had the battery pack connected together with that old monstrosity of lead-acid battery at parallel, which still had some charge left and also acted as a buffer.

It would be completely different story having the lithium battery pack connected as the main and ONLY battery and cranking with it four times a day.

A typical car battery can begin at 55 Ah 12 V, this is for a European downsized petrol engine (larger engine requires more, diesel requires more, electric accessories require more) from before the advent of start-stop systems (start-stop requires better batteries or even two of them).

That is 660 Wh.

I guess the weight and volume of this in li-ion would be similar to or slightly better than lead-acid (imagine roughly 10x laptop battery or 75x 18650 cell), but the cost would be a multiple even at manufacturing prices.

Next, the car battery can sit in freezing cold for several days to weeks at -20 °C and still crank or it can be frying itself all day under direct sunlight. This is deadly for li-ion. Electric cars have heating and cooling systems for the battery packs even when the car sits still in a parking lot.

Also, while driving, the battery sits next to hot engine. You can move the battery elsewhere (driver seat or trunk, like the second battery for start-stop systems), but you need high-energy leads and the engine heat is actually a benefit for recharging the lead-acid in winter.

Compare all these complications to price, simplicity and reliability of nicely recyclable lead-acid box...