Avatar the last airbender campaign advice.

[Darksteelhorseshoe]

Im running an Avatar campaign for some friends set about 75 years after Korra. Im using pathfinder as a base as its the system im most familiar with but am moving over some elements from 5e for their comfort(such as advantage disadvantage system). Its their first time in pathfinder and its my first time dming but ive played a lot. I need advice on certain balancing issues though. For the benders i am using the occult class kineticist and then will be making some changes at level 7 when they would normally pick up another element i want all of them to be about on par but some parts dont seem very balanced between the elements such as (mainly) the defense wild talents. The waterbender has an amazing boon to ac while the firebender deals a little damage when people physically. I had them do a battle royale for the first session to get a feel for where everyone was and the earthbender got taken out super easily when i expected the damage resistance they got would make them one of the more formidable fighters.
Any other advice on things to balance or change would also be appreciated. I have one of each bender and two nonbenders (a gunslinger and a ki blocker ninja) as well but ive played both of those classes and have a pretty good idea of what i want to do with them.

[Chess Pwn]

well if everyone was a kineticst then the earth has 2 problems
1st is if they were using elemental attacks (fire, cold, electric) that bypasses their DR so it's useless.
2nd is even if they were doing physical attacks, kineticists use the one big hit plan, which makes DR less useful. Cutting 5 off a 50 damage attack is hardly noticed at 10% reduction, DR is planned for more hits, so like doing a full attack and each hit doing 25 means DR 5 took of 10, which still isn't great but better at 20% reduction. Or against a many hitter like a claw claw bite or TWF when it's now DR 5 against 4 hits for 13 damage is negating lots of the damage almost 40% reduction.

So their DR is pretty useless against kineticists. The air I imagine would do the best since their defense would negate attacks thrown at them. The earth would do the best fighting the gunslinger or any other weapon user as they do many attacks for less damage per hit.

[Dαedαlus]

I think you're better off using the 3rd party Spheres of Power in this case. They have options for elemental blasting that fits more with ATLA mythology, plus a relatively simple magic spell point system that works great for beginners.