You're still using the passive voice. It's not as if "product managers" are some well-defined group of people. For that matter, neither are "bona-fide security researchers".
When I used the word "researcher" in scare quotes before, I wasn't trying to say this guy is quack. He obviously isn't. But using the word researcher is overblowing things. In reality, these guys are inspectors. They find real problems, and that is important, but very few of the problems they find are novel in nature. We do continually get the same types of defects reported, so something is wrong, but it has nothing to with reporting strategies. Change the way we write software--that would be actual research.
The disclosure trade-offs you describe sound plausible, but don't account for the fact that an inspector may find an issue no one else has discovered. They are also backed up by zero data.