No one was doing day one launches of big budget games on a sub
True, GP has been the first one to put AAA games day one on a sub. It's the new thing they added compared to game subscriptons released / announced before. The are also other things that GP implemented them before, even if Sony announced them as their long term plans back for PS Now in 2014 and seems that will be released during this year.
PS+ and Gold are forced for users that want multiplayer, there is no option to purchase online privileges on a title by title basis, those are different type of service being sold to a much more captive audience. That's a big distinction because GP subscribers want to have their GP sub based on the value offered, where as Gold and PS+ subs are just on there because that has become an accepted penalty for playing online on console (though they do give the games as perks).
If Spartacus is real, meaning they merge Plus and Now on a multi tiered service that would have a new intermediate base Gamepass like tier (plus the PS Now would be like the GPU one, meaning it also includes Plus) I think MS will follow rebranding Gold to mention it as a another tier of Gamepass so to bump subs count.
MS and Sony frequently make some moves to match the offerings of the other one, as already happened in other cases when Xbox removed the need of Gold to play F2P games.
Regarding this topic, I think it's also important to see if Spartacus mid tier -the base GP one- will also include PS Plus. If this is the case, then I assume MS will end including Gold in base GP. I think it makes more appealing the package and also makes it easier for the mainstream casual user, who may assume that if you pay to get some games that payment would also include to play online.
Can't remember very well the results, but as I remember there was a PS Plus survey and I think the main reason to get it was the games, with a 40% or so of the votes (so I assume it's why they added PS Plus Collection to PS5 and why they would be planning to include a base Gamepass like tier, which I assume would be more expensive than the base PS Plus sub). But yes, obviously the people who plays MP they get Plus/Gold for that reason.