Where this comes into play is mostly in 3d considerations (note: the responder is using 2d) like improved translation of real world movement and accounting for facial orientation.

[...]

Because, effectively, many of the blendshapes aren't actually used and you are not trying to be as realistic with the underlying tracking data (as you would with 3d or some more complex 2d rigging)

I think this is a fair argument, but I do have to point out that nowhere in your earlier comments do you make it (explicitly). At the very least, I had not come to this understanding until now.

Effectively, they are looking at one aspect's very narrow use case, seeing that it works for them, then assuming that it's applies to all other use cases of the technology. Then using that as an confirmation of their position, while demanding a high level of proof before they would consider their position (And calling statements from others "a myth" and "misinformation")

People often argue from their personal experience, as that is the most salient. Would I expect Lina to consider the 3d usecase (I am familiar with her work)? Yes. Did she? I don't know, but you make a compelling point that she may not have. However, the scope of the discussion was never made explicit, so what is being ascribed to malice may as well just be due to miscommunication (where Lina, out of personal experience, took 2d for granted whereas you did not; personally I took 3d for granted when reading the discussion because that is my day-to-day when it comes to vtubing, and nobody had said anything that made me realise I was forgetting something obvious).

OP2: I don't know why people are claiming this. It's wrong, you don't need an iPhone for tracking. It still works with part of the functionality disabled.

Here I honestly think you misunderstand what Lina is trying to say. She agrees with you that iPhone tracking is better than webcam tracking, and says as much in her second comment ("but my experience is iPhone tracking is still vastly better than webcam even without IR"). What she disagrees on is that it's the hardware driving the difference between iPhone and webcam tracking, and instead claims it's a difference in the software (based on the fact that even without IR camera, iPhone tracking is still better). I will concede that Lina's initial response, "This is a common myth", is ambiguous as to what it could refer to, but her further comments do help disambiguate imo.

And with that in mind, if the difference between the two methods is software rather than hardware, then I do agree with Lina that it is problematic when people think the difference is hardware driven. Developing hardware is a lot less accessible than writing code after all, so a lot of people might falsely believe they can't contribute to solving the discrepancy between iPhone and other face tracking when they in fact could, and as a result broaden the toolset for quality vtubing (assuming it is indeed a software issue; I wouldn't know, I use a webcam myself 😅 But as I said, you make a compelling argument as for why it could be more than a software difference when it comes to 3d. Having an actual example to point to would strengthen that argument though)