Fire does have one good use, and that is when you fight a NIN on your own. The DoT itself breaks a NIN out of stealth so going for a quick 1 stack Fire Superflare is a reasonable choice when u think that a NIN is about to dip out. Freezing him does keep the NIN locked in place in that situation, BUT he keeps the Stealth effect since it seems that only damage effects actually break it.