Let's be clear: this ability isn't used to have perfect information on how users interact with your product.
It's used to allow publishers to make more money from their consumers through advertising.
It's used to allow publishers to make more money from their consumers through advertising.
Additionally, cross-site tracking isn't used for feature/usage tracking. It's used for highly targeted advertising.
My point was the "shattering advantages" are really advantages for advertisers, not web designers.
This technique wasn't developed with web designers in mind, so let's be clear about that.
EDIT: But apparently no one cares, and will listen to whoever talks like an authority.