Yeah, your not wrong (about the data). The new client also trys to enforce not reusing addresses now, which means best practice makes it impossible for a parser like this to associate an address to a wallet.
Its accurate on a per address basis.
The data is interesting but useless if your looking for the biggest wallets. It can tell you broad things, like there are 200k addresses with unspent outputs (just a made up number), there have been a total of so and so addresses since the beginning of the chain, etc. Interesting, useless data. My favorite kind