I’m not sure that it’s ownership is the reason for The Guardians success. NYT has also been successful with a more traditional ownership model.

Their success, I suspect, is due to being early to shift from addressing a particular geographic market, to addressing an ideological market, after the internet destroyed the geographical barriers to entry.

I suspect this internet driven incentive to focus on ideological markets is a big part of why politics in most countries has become so partisan. When newspapers focused on a particular geography, but had limited completion, they had an incentive to avoid becoming partisan because that would only serve to limit their addressable market.