I take issue with a few of your points:
- Your insinuation without evidence that there is an alternative understanding of Rav Moshe's psak, there is no disagreement among his talmidim.
- Calling the poskei hador from the past 2 generations "unconventional" in a derogatory manner.
- Your definition of a "serious kashrus expert" is someone who goes around telling people which hashgachos they shouldn't use, but there are other experts who don't. (If @moko shows up again, he can verify the one I have in mind)
- You give more credibility to "kashrus experts" than halacha experts.
- Do most people ask "kashrus experts" because that's what they were taught by their Rebbe or Rav, or because that's what everyone does and it makes them feel more frum to say they only eat "top tier hechsherim"
None of this is directed at anyone in specific, and I'm not trying to demean any kashrus experts.
I was just stating the facts, Reb Moshe's enormous gadlus notwithstanding. This isn't followed or advised by anyone familiar with the kashrus field today (besides one "expert" you won't name), and the esteemed RY you follow, as a gadol as he is, seem to be a outlier in this regard. Also, Rabbi Elephant will NEVER mention a name of hashgachos people shouldn't use, nor will any respected Rav hamachshir do publicly. The notion that people deciding on their own to be makpid on top tier hecsherim is just to feel good, as if this isn't something that halacha experts are always promoting is just ridiculous. A sincere Rov will always guide and promote to look for the best hechsher possible, and not to rely blindly on everything that has a "Badatz" symbol on it.
Re:Timtum halev, it's well known that Rav Moshe said he's arguing on the Meshech Chachmah
As well as on the Chasam Sofer, the Ohr H'chaim, what he brings from The Arizal, and others too. On Timtum Halev matters they have the final say.
My point is that despite the fact that you may and you should follow your Rebbeim, you gotta realize that most people do look for the best hechsherim they can get. Most aren't okay with applying chezkas kashrus to the ability of guaranteeing top kosher products in today's extremely complex and advanced kashrus world. And most people do acknowledge that there are "mediocre" hechsherim out there which they'd want to avoid. Harping time and again with this דעת יחידאה just makes no sense at all.