With BC it’s arguable having more gens BC is stronger then more games within the same gen they share BC.
But Sony technically isn’t trying with Ps Now and GP is in fact pulling ahead. 2 million after 6 years to GP 15 million after 3 years. And it’s not about most titles, it’s about more new/recent titles.
With them going back farther, you could argue that the older the game is, the less value it has to the market and consumer base. You can chose to look at it however you want, so of course you're gonna go with the version that makes Xbox look better.
One of these services has...what...2+ million subs(?) while the other has over 15 million. PSNow is entirely irrelevant compared to Gamepass, and that's despite being around for longer, and by virtue of PS4 being the dominant console platform this gen, having had a lot more potential access points in people's homes (something which is going to be changing now that XCloud is getting up and running). And MS accomplished this, as the ardent PS fans love to remind people, without even having a large library of consistent first party output to support the service in a way that would be optimal for sustained growth. That too is going to change this gen, with all the investments MS has made over the last several years.
So...if you wouldn't call that pulling way ahead, I'm not sure what you'd call it.
The difference is almost certainly in marketing. With Xbox it's everything because it's all they have. They push it at every new game reveal, every event, every commercial. I keep forgetting PSNow even exists half the time because Sony doesn't focus on it. Sure, I will concede that Gamepass is the more popular of the two services, but it's still a clear case of 'if it mattered as much as you say, PS4 wouldn't be outselling Xbox like 4:1 every week'. Gamepass is good. IT's better than PSNow by most metrics, this is clear. but to dismiss my stance of them being similar and Xbox not pulling ahead despite their better service? Naw, don't try to pull that narrative because Xbox is doing better in one category out of like 12.
I've never said GamePass is bad, but PS has a similar function, but people on PS don't bother with it because they have too many exclusive titles to play that aren't on it. Clearly this business model is working if PS4 is still doing so well. Gamepass might actually be hurting Xbox in the long run, as it gives people less incentive to buy games.