Alice and Luna are both new students at the Academy. I don't think they will start out teaching them offensive and defensive spells and recipes in the first year. Luna even says it takes years to master one magical affinity and she has two to master. She was given a task way over her head to save her mom, even though we know had she broken the "curse" her mother would have been eliminated with Luna.
Alice knows plants from her time in the village but has come to the Academy with no practical experience and yet, she was picked to be the instructors assistant. She will grow in knowledge and experience and before long, she will be creating new potions to help the MC.
Sylph is young for her race and has been on her own for a long time so hasn't had the benefit of a mentor. She has been basically hiding out with Dalen at the guild since she joined up with him. Now that she has bonded with the MC, she has incentives to break herself out of the rut she has been living in these few years.
Eliza was naturally agile before her transformation so the extra strength, speed and stamina are helping her be better at combat then the other three. No, she wouldn't last long against Diana, mostly because she would be like the MC, and would not want to hurt her, just disable her unless she thought that Diana was a threat to the MC.
I think all of them will get better as they gain experience.
Diana is definitely the most powerful of the potential "human" LIs. But she also spent the time since she was a little girl and watched her father be tortured honing her skills. And she is naturally powerful. The MC fought her to a draw that almost killed her, I don't think the MC was at that state when they were pulled from the water. He knew nothing about her so was constantly surprised at each of her new abilities so was a little off balance. But he didn't want to hurt her either but as she kept escalating, he had to as well.
My MC recovered faster than her and healed her before she woke up. Yes, walls of dialog wouldn't have been as much fun as watching them battle it out, but that could have been avoided had they chosen to talk it out first.