From my experience playing guitar, the average punk or metal song is almost entirely power chords, while this data says power chords are only 5% of chords in both genres...

I thought maybe there's types of metal and punk that I don't know about, but Wikipedia, LLMs and guitar tab sites all agree with me. Punk and metal is overwhelmingly power chords, so I don't see how the data comparing chord types can be correct.

I guess one aspect missing here is weighting more popular songs on that analysis.

I assume that the analysis is simply counting every song chords, so a unknown band you've never heard about has the same impact as The Ramones.

I'd like to see the same graph weighted by band popularity using either YouTube or Spotify data.

That was also really surprising to me, but I think it can be explained by the fact that they bundle up repeated chords.

You could play a G power chord for 3 minutes straight and it would count as one.