Agreed. Mass in a wheeled vehicle matters most when stopping and starting (and to some degree climbing). Range matters most at high speed, and at high speed wind resistance is far more important than mass.
To put it another way, if you literally doubled the Model 3 cell-level energy density you'd shave off under 200kg from the vehicle's mass and cut the energy consumption by ~4%. Meanwhile, if you were to instead halve the cell cost you'd cut about $3-5k off the vehicle's production cost. Gee, I wonder which would make a bigger difference in the marketplace... 200kg weight reduction / 4% efficiency improvement, or a $3-5k (plus margin) discount?
Or to put it another way: you could instead put that $3-5k back into the vehicle and build the vehicle out of lighter, more expensive materials, and you'd save a lot more than 200kg! An alumium body-in-white costs about $600-800 more than a steel one, while a CF body-in-white costs about $1200 more.
It's price per kWh that matters more than anything else in the automotive industry. A reduction in price per kWh means you can also increase the number of cells, simultaneously meaning more kWh, greater longevity, faster charge rates, and more power. Higher energy density does not, and often comes with just the opposite (some of the biggest problems with new high-density techs relate to cycle life and C rates)
Only in aircraft (and in oceanic transport / deep sea fishing, at least until floating gigachargers become a thing) is the key enabling tech for going electric "improvements in energy density".
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