Huh... I'm super liberal (not so progressive necessarily) and I enjoy Ground News a lot. I don't feel like it gives an impression of both-sideism at all, and that's something I'm quite sensitive to?

That is their stated purpose, though? To give equal parts left & right so that you can supposedly be better informed. But the implicit assumption is that left & right are equally truthful & fact based, which is not the case, so the resulting coverage leans right.

Notably, like another allegedly unbiased news source (RealClearPolitics and related), Ground News is run by conservatives. They know precisely how it works and are taking advantage of sensible people who think they must be getting biased news and want more exposure to the other side, with the intention of ratcheting the Overton window ever more to the right.

No, I don't believe that is their stated purpose. It's to share stories from across the spectrum and then emphasize how differently they're reported or not-reported.

That does not necessarily imply giving equal airtime or equal legitimacy to the different sides at all.

Eh, to the extent that I care about it being "run by conservatives" it's only in whether it creates a distorted perception of reality. As someone with a very varied media diet I don't really find them to be distortive, so I don't really care whether the founders are conservative or not.