Not that it’s canon anymore but the Legends continuity clearly established it as a definitive light side power and had Jedi that were dedicated healers, but no one complained about it then.
I didn’t know about that. In that case, that’s dumb too.
she studied the ancient Jedi texts which might have included techniques and things that were lost
I doubt anything could get “lost” in the Jedi archives. They had the largest library of Force knowledge in the galaxy, if Force healing was a valid power they would know about it.
Rey was able to manifest powers like force lightning instinctively because of who she was, so it makes sense that she’d have the other side of the coin.
Force lightning is a dark side power, she has it because of Palpatine. I doubt Palpatine could use any light side powers.