Warrior: Nerf Brann so that it only triggers when he is on the field or for X number or turn (possibly 2). Armour gain reduced by half and increased cost on control cards.
DK: Plagues cards only put 1 plague. (So the rest of the classes deal with the amount of plagues that dk can discover and use).
I think hand buff is fine. I would just change something like that all the buff cards have a corpse requirement or that quill only affect minion.
Mage: Needs a complete rework, no minion is a joke. I would remove those cards from mage and replace them with other cards. No one is ever going to use them. Spell mage otk was very slow compared to other classes but I think it should have a way to reduce spell costs so that blizz could nerf sif / mage since mage cant keep up with all the armour gain, buffs and aggro decks. give them stronger cards and stop the no minion cards and rng. Include cards that buff a specific spell type so mage has more variety. Azerite Hawk now discovers a titan (Personal Preference).
warlock: just nerf minion stats.
hunter: Increase spell and minion costs. Just to tone down the aggro a bit.
Chaman: flash of lightning only reduces the cost of the next spell.