Fire has a ton of damage and one of the passives deals bonus damage every time you use a skill. Plus burn will do more than a ninjas skill so when you attack with a skill that burns its worth twice what other skills are on a single enemy. plus burn stops heals from working on that enemy which lets you focus fire one enemy to death.

kankuro's puppet also dies from one attack of a fire skill which reduces his ability to tank completely if you use the 2nd esoteric.

I will admit that fire isn't the most well rounded(ok hes not anywhere near balanced attributes) but if your goal is hit em hard and hit em fast then fire is the way to go

you dont HAVE to use the damage passive, its actually better to not use it outside of kyuubi since the other passive on that line reflects enemy effects and increase damage against burning enemies, just like the damage passives for the other classes arent amazing. I mean sure 40% to 3 ninjas is nice, it's essentialy an extra attack each turn but when the enemy uses cc I would rather have the reflect as that gives me more damage and makes me take less damage.

Plus kekkei genkai users are common and easy to obtain, Sasuke is from a mission at like lvl 3, Kakashi is gained on day 7, haku is also gained day one, hinata and neji arent hard to get either and they c*l combo together easily, Plus after them there are others which you can work towards.

main sasuke hinata combo great

most of the status effects the main characters inflict are the same float flight repel, the only combo effect fire doesnt have is knock down which only earth and wind have.

I don't know why you are saying it doesn't combine well or that it has to be used with kekkei genkai users.