Yes - I agree.
It's much more complex than just "left" and "right". And the definitions of "left" and "right" are not well defined, and changing.
I suppose the well intentioned folk at Ground News are just trying to offer a bit more meta-information to give news-readers better context on their news sources.
In my opinion, all that complexity and lack of clarity and consensus doesn't make it worthless. I can agree with them in broad strokes that Fox News is on the right, and dissidentvoice.org is on the left. I can agree with them that the BBC is comparitively more in the centre. I can also look into their methodology for rating bias and generally agree (while possibly disagreeing with minor points). And importantly, when the bias rating is disputed I can take that into account with the appropriate weighting. e.g. If Fox News calls the BBC a far left organisation, I might take that with a grain of salt - They would say that. But if the criticism came from a more centrist source I might give the criticism more weight.
In summary, I think this sort of bias rating information can be helpful, if used appropriately. But the way I would use it is not to fill my blindspots on the far left or far right, but more to ensure I know which sources aim to avoid bias.