Superman isn't weak against lightning. It's shown on panel that it barely affects him if at all. When he fought Livewire, he was weakened by his battle with the Queen of Fables to an insane degree, and she still couldn't put him down. The other most notable time by the dam, he was still regaining his powers. Livewire has yet to take on a fully powered Superman.
Captain Marvel's lightning is magic based, and it is the magic aspect that hurts him, not the fact that it looks like lightning.
also, lulz at Superman not having to learn from Diana. Please. She's a better fighter. He can learn something from her. Same goes for Batman. All the strength and speed in the world aint shit if you can't use it properly.