Why is it useless?
Google at least lets me back things up.
Most services do not allow it at all.
So there's no restoring anywhere else at all, no chance.
Having the data I could at least have a chance that some service might offer a rebuilt import option to pick up those google users ... or I could build it myself / at least have the information.
To me that's still leaps and bounds better than any other options that I know of.
For all other companies, at least if you are in the EU, you should he able to request the data by eg email and they are obliged to send it. You just don't know what format you'll get.
As for all other companies they might be obliged to send it, but I don't see many ways to do so.
That still make's google's method way better IMO.
Google Voice exports your texts into a clumsy pile of HTML files. That's why I wrote a parser to convert all of your Google Voice messages into structured data.