In most circumstances, being faced with hundreds of weaker demons was not a problem that Blake would concern himself with.
His and Cyra's dark flames were the perfect tool to wipe out a large number of enemies by simply staying still in their place and throwing dark flame fireballs everywhere. Blake would need to also fly and maneuver in the air if the enemies were like the horde of bison that recklessly charged forward, but if it was just a random horde of humanoid demons, then he didn't even need to bother moving from his place to deal with them.
However, that was in most circumstances. Right now, not only did Blake and his group were located right in the middle of their enemies, not in front of them, which means that they need to constantly keep in check of all the directions around him to keep his enemies off bay, but they were also being threatened by stronger enemies that couldn't simply be dealt with just using a few spells.