Nowhere is the faction innately restricted to that description in lore. Indeed if it was then the Magmadroth wouldn't have been created as a unit because it helped stop the army from becoming exactly that.
Magmadroths are the literal only exception.
But even that GW screwed up by having the "juveniles" be ridden by runesons, as opposed to having them be something properly distinct.
If you start playing that game then you can say that Flesh-Eater Courts could be similarly restricted to 'Deluded flesh-eating Ghouls', Kharadron as 'Dwarfs in diving suits' or Daughters of Khaine as 'angry naked Elf lesbians', yet GW have developed the latter two beyond their starting range (and may well do the same with the former with their upcoming model update). Exactly the same thing is possible with Fyreslayers, they just need someone who has the creativity to think of the ideas for them.
All of those have more flexible themes than Fyreslayers (in its current form)
FEC are deluded into thinking they are noble knights, you could make a FEC equivalent of every single CoS unit, from the lowest infantry man to the most regal knight, without it breaking the theme.
KO look very similar visually due to their diving suits, but they have a technology theme which makes it easy to invent new units if need be.
You don't really need much more than 1 or 2 lines to explain a new unit for these two.
E.g. adding FEC cavalry is trivial, all you need is to put some ghouls on some kind of undead beast that's roughly horse-sized and write 1 line of text explaining they think they're noble knights charging into the enemy. That's it. Want heavy cavalry? Slab some rags, a skull helmet or some rusted armour on them and give them an actual weapon to hold. Light cavalry representing lesser squires? Have them be mostly naked wielding bone clubs. Want a trumpeter who signals to a noble's hunting party where the prey is? Stick a varghulf on a horse and say the FEC thinks it's shrieks represent trumpets. And you have precedent for all of this, as the FEC riding zombie dragons and terrorgheist literally use a similar explenation of them thinking they are regal kings riding majestic warbeasts.
FEC have a pretty strong theme overall. GW just doesn't do much with them, which is a shame as they're the only vaguely interesting undead faction that doesn't just have to blindly follow Nagash.
DoK are indeed similarly one-note as the Fyreslayers, but they at least have some mutations with snake people & winged people in their ranks. Which at least gives them something to work with as they can always introduce new snake-based nonsense.
There are many things that can be done with the Fyreslayer army as I have said several times before, particularly if you look at the Warhammer Fantasy Dwarfs for inspiration, but as the ultimate Fyreslayer critic you're blind to using a bit of imagination with them.
O there's things you can do.
But most of them will require somewhat of a retcon to not make it feel somewhat forced.
E.g. Other vulcanic creatures could work, but raises the question why they are suddenly beastmasters, since currently they pretty much exclusivly raise magmadroths. Similarly, any new technology, like a chariot or artillery piece, would beg the question where they got that from as currently they basicly don't seem to use any technology besides axes.
I'm not saying it's impossible, I'm just saying that it requires a lot more lore to introduce a truly new unit compared to other factions.
And yeah, GW is failing to use the potential Fyreslayers have. But if they want to use that potential, they'll first need to open up the lore a bit to actually allow for these different options. And that would be a pretty major release, similar to our update, or what's currently happening with CoS.
So as long as it's just minor updates, I fear you're stuck with your angry naked dwarf footheroes. There simply isn't much you can easily introduce in a minor release like that for fyreslayers.
Everyone's behind it, everyone wants it, we just want GW to DO IT! And do it right!
Carefull with that monkey's paw
