Only 6.5% solo stakers on Ethereum???

Is this true? Of the 500k validators, they estimated that 6.5% of validators (by index/pubkey) were solo stakers on the Beaconchain based on a confidence score of 50% or greater. 3.3% were strongly predicted as solo with 99% confidence or above, 1.1% were 95% to 99%, 0.35% were 90% to 95%. If solo staking is a core design principle, and only 6.5% of stakers are solo stakers, then what happened to the core design principle?

https://blog.rated.network/blog/solo-stakers

EDIT: BTW, this 6.5% includes RocketPool, which is considered "solo" staking for purposes of this study. So... dayum.