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.
I think a big part of it is that the internet made the existing leaders into massive winners, a bit like how the teams at the top if the first division managed to cement themselves in the premiership when that happened.
If you were to name some important newspapers in 1995, you'd probably also have the Guardian, NYT, WaPo, on your list. They just pulled away from the pack due to the was reputation works in the internet age.
And yet the LA Times and the (London) Times and the Chicago Tribune did not, so however true this is, it took some extra magic sauce to "pull away from the pack". It wasn't just "being an important newspaper in 1995".
I think of it as a necessary, not sufficient condition. Same as with the football analogy. Everton and Spurs were in the premier league when it started, but they're not considered the cream of the crop.
Checking the other side of this, what media properties did not exist in 1995 but are a world class now? Not too obvious to me.
The guardian always addressed a left of centre audience even before the internet. The Telegraph a right of centre one. The print advert market used to sustain that.
UK press has basically always been partisan, which was why the Daily Mail was publishing pro-Hitler articles on behalf of its owner.
https://en.wikipedia.org/wiki/Harold_Harmsworth,_1st_Viscoun...
Or The Guardian supporting the Confederacy[1].