I would hope that it would take a weaponised gust of wind that could knock confectional forces off of their feet(which would be an expoiltable vulnerability, but they should largely ignore being cut with a sword, so it is trade-offs...), but bad rolls are bad rolls... Even if they can be gusted-and-dusted-to-custard, they are still extremely irritating until such a gust appears, so relevant, could typically take shelter so as to not be completely exterminated, and could be revised to be less vulnerable to such things.
I would argue that the imps are ineffective at penetrating enemy lines, reduce the effectiveness of blackscale formations they integrate with, and aren't fast enough to intimidate through positioning. In heavy armour they are heavy infanry. Not GOOD heavy infantry, but they are a starting unit. Likewise they are somewhat bad light infantry in light armour and somewhat bad archers with ranged weaponry. They are a generalist starting race with high potential(from the currently-useless? fire affinity and magical equipment). They are sort-of-bad at everything but functional. The balckscales are far more intimidating as heavy infantry, and could take the role in a pinch, but I suspect that their biological systems are lacking the endurance required to hold a line for literal days as one might expect of a truly epic battle of the champions of the gods...
If the Ravens match the description, they should be very tenacious, inherently disheartening, able to persist anywhere the enemy doesn't have largely explicit countermeasures, and able to pick apart weak-points of any units that possess such. My only real worries are specific countermeasures, such as radiant light-fields which would trouble us regardless if we are being thematic, and the high difficulty from having a somewhat new construction and a somewhat new fear effect, but I just couldn't resist the thematic elements...
We do, however, have many fine proposals left over from the previous round of voting. Grues are, well, I worry they are ill suited to Fire, but I like them otherwise... They would likely allow forces to be diverted from Earth to Fire... Seekers are capable, though very ambitious... Forging darkness could sole our problems with Fire's limited mobility if it works well, and also provide barriers against ambushes in Earth. Daemons can't fly, but could probably be thrown well enough to get work done in Fire, and I suspect that some of the fliers in Fire can only fly there, so maybe the Daemons could too? The Ballistae offers a ranged attack with a range and heft that the flame caster is lacking, being distinctly artillery, and offers research into mechanisms. It is a solution to the lack of reliable ranged weapons in Fire that would collaborate with the flame caster rather than replacing it. Any of these would be decent choices.
So yes, on a bad roll the Ravens would be very troubled. More so than a simpler design, but they really don't seem to me to be in any way redundant with imps.