The issue with cindercoat isn't the +fire, which is nice but to be honest not really unique and a bunch of other elements also get the same skill % from other slots, the issue is the ressource cost reduction which is a unique property only to fire and generally what makes the difference. That said, I don't think you're forced into fire as a crusader or WD because the fire stuff is simply not that great to make full use of the cindercoat.
WD explosive dogs has shit for aoe radius and a wonky hitbox/path(it spawns behind you and on the sides, so it's terrible to use in closed space or when you're surrounded by shit mobs) and that's really the only good fire spender, most bats rune are pretty shit compared to vampire bats or poison bats and locust is a one time cast, so it's kinda eh, whatever. Cold build or physical build(for pets) is a lot stronger for WD even with cindercoat.
As for Crusader, the only 2 fire spenders are blessed shield and hammer, and neither are particularily impressive, plus you lose a lot of damage from your cooldowns which are almost exclusively holy and physical(falling sword has a fire rune, the better rune, but it's one of the weaker cooldowns since it's 30secs with a 10secs ground dot for the same damage as condemn x2 and it also costs wrath to use). Blessed Shield Fire with the bouncing shield is pretty good though so I guess you could still build around that and make it work, but it's not massively ahead of running a holy shattered blessed shield or fires of heaven with the 3beam weapon.
For melees lightning builds with SoH also tend to be better until they fix SoH.
Still it's a big issue that the stat doesn't exist for other elements, or that some elements get fucked on element % mods. Excluding weapons since they tend to depend on class and shit, fire has 2 with cindercoat+magefist, frost has 1 with frostburn(one more if you're a wizard with the orb), lightning has 1 with thundergod vigor(but as a monk you can replace andarius with eye of the storm and get 10% more as well as a set bonus giving 15%), poison has one with poison waders and that's it. The only physical % is a 1H weapon, the only arcane bonus is a wizard weapon, holy has a shield but that's pretty much crusader only. Poison and physical are especially lacking, with frost, lightning and holy having several weapons each to compensate for the lack of armor slots(but since fire also has weapons, it's still ahead).
