Was curious about how the average power to weight ratio has changed over time and thought I would collect the notes from my Googling.
First, this analyses from Reddit that graphs power AND weight by manufacturer.
Not exactly what I was looking for but you do see Daimler and BMW fight it out for best ratios over time (see the animated version here).
Also found an academic paper with some interesting trends over time, including a European country comparison with Sweden coming out on top in terms of average power per car.
Seems like the data is limited to 1997, so I am curious how these trends have held up.
And finally, a graph of average power/weight over time... in Belgium. (The top line is for the best selling models.)
I am still looking for a more comprehensive analysis of how power to weight is changing over time, but I did run across this interesting spreadsheet from Exomotive showing power to weight for a sporting cross-section of cars.