O I'd assume they do have a bit more. Some lodges will be a bit more honourable, some a bit more greedy. There's bound to be some cool stories somewhere about a fyreslayer doing something heroic or whatever.
You're correct here - as a possessor of the first Battletome I can say that not all Fyreslayers are the same. Some lodges such as the Greyfyrd have adopted the whole mercenary idea as their way of life, and are less reliable than others like the Vostarg who are much more like the old Dwarfs in that they always keep to their oaths. Some even turn evil such as one lodge that became addicted to Ur-Gold and started attacking other Fyreslayer lodges for their Ur-Gold, and one of the sons of the Vostarg Lodge who was presumed dead after remaining to protect the Vosforge as a diversion to allow the others to escape but has since become a Chaos Dwarf, but then the regular Dwarfs in Fantasy had the same problem, because like humans they are not flawless demigods.
I don't own the Fyreslayers Battletome so I don't know, but I would assume that they do have a bit of a richer background story there, don't they? I mean: those names they have seem to suggest that.
For those of you who don't know, I'll give you a quick summary of the place of all the Fyreslayer units in the lore:
Auric Runefathers: The leaders of the Fyreslayer Lodges
Auric Runesons: The sons and heirs of the Runefather. Only the strongest and wisest Runeson gets the chance to succeed his father when the Runefather dies - all the others go off to found their own lodges.
Vulkite Berzerkers: Mainstream infantry, pretty much a combination of Dwarf Warriors and old Slayers lorewise.
Hearthguard: Protectors of the Forge Temples and the Lodges
Hearthguard Berzerkers: Bodyguards of the Runefather and his royal family - think Saxon Huscarls
Auric Runesmiters: Bog-standard priests of the Forge-Temples - responsible for forging the Ur-Gold Runes and distributing them to warriors
Auric Runemasters: Highest-ranking priests of Grimnir - responsible for governing the Forge Temples, advising the Runefather and searching for new strands of Ur-Gold
Grimwrath Berzerkers: Essentially the champions of the Lodge - these chaps have so many Ur-Gold Runes hammered into them that they have strength and resilience unmatched even by other Fyreslayers.
Doomseekers: Pretty much the AoS equivalent of Dragon Slayers and Daemon Slayers in Fantasy - they wander around seeking the biggest enemies to kill for the biggest payouts.
Battlesmiths: Fyreslayer Bards who recite the deeds of the ancestors to inspire their fellows in battle.
An additional nugget (see what I did there?) of wisdom about Ur-Gold Runes:
To paraphrase Obi-Wan, “Ur-Gold is what gives a Fyreslayer his power” - when an Ur-Gold Rune is hammered into his skin, the power of Grimnir from these runes supercharges the Fyreslayer’s strength and also supplements his life force so that he can endure wounds that would otherwise kill him. However, each rune only gives out so much power, and when the power in one or more runes is used up and dissipates into the ether to rebuild a bit more of Grimnir, the Fyreslayer has to have new ones to replenish his strength, so whereas regular Dwarfs gather gold simply to display their wealth, Fyreslayers gather Ur-Gold to ensure their hold’s survival. Without it, they are unable to lift their heavy Fyresteel weapons and are as unarmoured as a Slayer of old - that’s why they are so desperate to get it.
Hope that makes things clearer for all you Seraphon players out there who are new to Fyreslayer culture!