All the classes are pretty balanced out in different areas, such that wind & lightning are high damage causing classes, water and fire are control/condition causing classes, and earth is for defense.

Lightning is indeed a really powerful class, and I would say it's the one with the highest damage; it is also very easy to form teams with him with ninjas that are not hard to attain, so he is a very popular choice for many players.

a 2 star 9 tail naruto is not often used as he does not work very well with other ninjas, however if you are talking about 3 + star 9 tail naruto, he'll be a good one to use. gaara, i would suggest using him if you have a wind main, if not, it's hard to work with him.

would you consider scarlet blaze strong in the early game? yes, all the classes are strong if you have a good team and are tactical with your battles. any class will be able to beat all the other classes.

not being able to synergize with specific ninjas does not necessarily mean they are weak, you can't expect your ninjas to work with every main. There are certain ninjas that work well with certain classes, such as gaara, i would only use him with the wind main or in ranked battles.

Sorry if i have missed it but, i don't know what class you are, so i can't say whether subbing her in is a good idea or not.

for your first class change choice though, i would suggest choosing a class that has a different battling style than your current, such as if you have a high damage causing main right now, try a controlling class

this is the difference
http://oi65.tinypic.com/v6rzux.jpg

he becomes a lot more tankier, and his mystery just kills you in one hit.
especially with a medic on the team, you can never really kill him off unless your power is significantly higher.
i have tried it and got his life point to 1/4, but after that round his life point was restored to full health.
for most times when people see him in the arena or in pvp, they just know they are gonna die :'(
it's the you see you cry team lol
even with other kages and jinchuurikis on your team, it'll still be a tough fight

this is why it is very hard and very expensive to upgrade his stars as he'll is one of the strongest ninjas in the game.

gaara is a good ninja to have, but works better with the wind class
if you have other choices i wouldn't use him for the other classes expect for ranked battles

use the two cloning talents, and with gaaras shield and buff it'll be hard for your opponent to even get to you