Not really if you just increase the capacity of each cell you decrease the maximum power draw so the performance goes down.
If you just add cells you increase the weight of the car which can also have a negative or neutral effect on performance.
If you just add cells you increase the weight of the car which can also have a negative or neutral effect on performance.
If you have two lithium batteries which are identical with the exception that one is double the capacity, the larger battery will be able to provide double the current at the same voltage and thus double the power. Lithium batteries are rated for current draw as a multiple of their capacity.
Lithium batteries are rated for current draw based on their chemistry please do some basic reasearch.
And no if you have 2 identical 18650 they'll have the same density and sustained and peak current draw if not they are not identical.
Cell size, chemistry, internal resistance, breakage and short currents etc are all variables based on the exact make of the battery.