Each element should have a major and minor role to it that really encapsulates most of the fantasy.
Earth should be DEFENSE first with some minor AOE abilities. The AOE should for Earth should be the weakest AOE out of all the kineticists in terms of damage, but it can cause creatures to be prone if they fail their fort save. Their elemental blasts should hit the hardest.
Water should be AOE first and foremost. The most AOE out of all the kineticist packages. They have the strongest AOE potential out of all the kineticists. As a minor, they have some minor healing capabilities. Water has the strongest AOE impulses.*
Air should be all about fluidity and striking with elemental blast many times, but their elemental blast hits the weakest. They should have an ability built in that gives them the same bonus to attacking multiple times as a rangers flurry but without needing to use an action to target an enemy. They still only deal 1d4, but their second and 3rd attack only has a -2 and -4 penalty. They get better utility, some of the best utility out of all the elements.
Fire should be all about single target blasting with minor AOE capabilities. If you want a single target blaster with strong single target overflow abilities, pick fire. They also get minor AOE capabilities. They can be fairly strong and useful, but not as strong as water. Their attacks can also cause persistent fire damage. If you want a single target blaster that's effective, choose fire.
Wood should be the main healer out of the elements. Their major role is healing and support. Their minor role is immobilization and control of the battlefield.
Metal should be the opposite of fire where they are heavily focused on AOE damage with some minor single target DPS, but their single target isn't as good as fire.
Really lean into differentiating the elements based on roles to cover multiple different "styles" of play into one class.
And if people want to do multiple different roles, they can just use dual gate.
