(I’m going to soapbox for a minute, apologies ahead of time).
The issue with perpetuating this naming is things like this:
(Not bad vibes towards the author, this is just an example). People think that “immutable” a top level feature, a thing that must be classified and organized. So much so that the actual features of the thing is entirely overshadowed by that part of the conversation.
Ubuntu Core, Talos, and NixOS serve totally different use cases, but are artificially compared because they’re “immutable”. This constantly happens with bloggers and youtubers because everyone keeps talking about immutability as some kind of crux feature that determines how to classify a thing.
For example, people routinely put openSUSE Aeon and Silverblue in the same boat because they “are immutable” but are very different underneath. If you asked someone to compare the two I would 100% believe that they would put openSUSE Tumbleweed and Workstation in one pile, and then Aeon and Silverblue in the other pile.
This doesn’t really make any sense! People ask me constantly about my opinion on VanillaOS. How am I supposed to know, I use Fedora! But they’re already trained to think that the “normal” distributions are one set, and the “immutable” ones are a new top level primitive.
The “immutable” episode that The Linux Experience did is a also a great example of how the branding has confused people. For some reason the episode ends up being about how “immutables” are confusing and limiting because each one is different and there’s no one way to do things and now everyone is confused.
And check this out if you haven’t seen it yet:
All of the actual benefits of this model (composability, reliability, reproduceability, etc/) – the thing that we need people to actually understand are being underserved and not being explained, which is a tremendous lost opportunity.
Even Fedora’s issues and docs imply that they’re way more different than they really are. For example I read one the other day about toolbox (can’t find the link) where the description for a new feature was “… this feature is critical for the adoption of immutable variants.” when instead maybe the descriptions should read “… this feature is critical for the adoption of Fedora.” 
EDIT: I also think it’s great that people are at least talking about it more, I think this excitement is great! We just need to figure out how to get a better message out because there are many awesome features that people are totally glossing over because they get stuck here.