The discussion was directed here from the other thread so I brought a quote from @ridley with me.
I agree that most of the international fandom is using the term honmei wrong. Online I see most people use it to just mean “favourite” when it actually has a much deeper meaning. Although not quite, because it seems some of the original connotations are still there, like it is generally agreed you can only have one and there is an expectation that it never changes. I see this constanly causing problems when people call their current top favourite bandman their honmei and then have a whole crisis if they start liking someone else more.
Now I absolutely do not claim to be an expert and I might be talking completely out of my ass but I also don’t think that what @ridley and @GreatNorthernVK described above is quite what a honmei is either. I think those describe just the general oshi-dynamics. You can have multiple oshis but only one in each band and yes, it kinda has that host-dynamic going on based on what I have heard.
But to my understanding honmei is still a bit more than your “top oshi”. An oshi can definitely develop into a honmei and depending on the person/band, there might a personal relationship there as described by @GreatNorthernVK but I don’t think it is necessary.
My understanding of honmei is more like a “soulmate” through art. Not in a delulu “I am going to marry him” -sense (although I am sure you can find those types too) but in the sense that you feel a deep connection to their music, concept and art in general. Probably to their personality (what you know of it anyway) to some extent as well since I find it difficult to imagine feeling that deeply about someone’s art but disliking them as a person. Art is a way to express yourself after all 
And that is why not everyone has a honmei, you generally can only have one and it very rarely changes.
Typically you will also go out of your way to support your honmei but it is genuinely hard not to if you feel a connection like that to their art. Some might also have a more personal relationship with their honmei if they are small enough that you get to interact with them regularly but that is probably not possible if your honmei is someone like Gackt or Kyo. And yet I am certain their art has touched more people than a tiny Vkei group still doing only taibans (no hate, I know there is amazing talent there too but this is inevitable just based on reach).
Like I said, I do not claim to be an expert and I am not quite sure that there is one completely agreed upon definiton among the japanese fans either because that’s just how terms generally are. Like if you were to ask a dedicated bangya in the dominor scene they might scoff at the idea that you could have a honmei you don’t meet regularly. But then an older ex-bangya who lived through the glory days of MM and still dedicatedly follows everything Gackt does and draws comfort from his music daily might be equally offended by the idea that someone could have a honmei who learned to play the guitar seven months ago and whose band has only released three songs
Oh also @KDJ since you were part of the discussion in the other thread.