The P0 disclosure is the disclosure to the good guys and users.
You're assuming that the bad guys are learning about the problem from P0's disclosures, but without P0's disclosures, the bad guys would still learn about the old bugs from the patch itself.
So which is a better situation: a world in which only the bad guys get the information about broken old versions, or a world in which everyone gets the information?
The way I'm suggesting you measure "better" by measuring actual hacks, and how the number of actual hacks is changing based on whether you insert a delay or not.
So we go back to my question above, which you didn't address. I'm saying the fact that patches come out on a regular basis means that people would still have to update regularly, even if each individual patch comes with a delay before a PoC etc. is disclosed. So I repeat the question: would customers really update regularly but actively filtering out patches whose disclosure deadlines haven't passed? If not, why wouldn't the delay that still achieve the outcome everyone is asking for here?
As noted elsewhere, patches are effectively disclosures, with some small delay (best described as an obscurity delay) baked in.
And wouldn't a vulnerability still be there even if there wasn't e.g. a PoC disclosed? I'm not really sure how that affects what I'm saying.
Of course not, that's a straw man that only you are suggesting and often isn't even possible on most systems. People by-and-large will apply all pending updates at once.
Responsible disclosure pushes folks to update. Well, that and new emojis that they're feeling FOMO from. It's a carrot and stick sort of operation.