The power of dice compels you!

“Especially important is the warning to avoid conversations with the DM. We may ask what is relevant but anything beyond that is dangerous. He is a liar.” -Merrin, Cleric of Tymora

All classes have their strengths and weaknesses but some are known to fall behind the mathematical curve. You could change class features but I find it’s easiest to make balance changes with magic items. They’re easier to justify within the lore, easier to change or remove and can be tailor-made for each player. When our Phoenix Sorcerer almost burned herself to death, I felt it made sense to give her fire resistance. She’d later find a family heirloom, made of red dragon scales, that did just that!