That is not even comparing apples to oranges, that is comparing apples to steel. You are correct in that energy density does not matter very much for weight-insensitive generation such as grid-scale generation, but energy density matters for weight-constrained applications such as airplanes and rockets as the poster mentioned.
However, assuming that the renewable generation cost curve continues to improve exponentially then the most likely outcome for a carbon-neutral or carbon-negative future will be using electricity to manufacture high density combustible fuels out of atmospheric carbon, effectively using it as a high density "battery" for use cases that demand high energy density.
To the extent that your analysis is relevant to the concerns of the poster, all it means is that batterys are actually ~4x better than the raw energy density would indicate. As to the specifics, Wikipedia claims petrol is ~12,888 W*h/kg or ~24x the battery energy density in the article, so ~6x better with respect to car motion. Note that the current curve has only gone from ~100 W*h/kg to ~500 W*h/kg, so we would need to see density growth comparable to the last 30 years to happen again.
However, assuming that the renewable generation cost curve continues to improve exponentially then the most likely outcome for a carbon-neutral or carbon-negative future will be using electricity to manufacture high density combustible fuels out of atmospheric carbon, effectively using it as a high density "battery" for use cases that demand high energy density.
To the extent that your analysis is relevant to the concerns of the poster, all it means is that batterys are actually ~4x better than the raw energy density would indicate. As to the specifics, Wikipedia claims petrol is ~12,888 W*h/kg or ~24x the battery energy density in the article, so ~6x better with respect to car motion. Note that the current curve has only gone from ~100 W*h/kg to ~500 W*h/kg, so we would need to see density growth comparable to the last 30 years to happen again.