Here is how I will change the game if I was the lead on the balance team.
Remove keystones and go back to the old mastery system. Remove first tower gold. Bring back fortification on the bot turrets. Remove elemental drags and bring back the 5 drag system. Change lethality back to standard armor pen. Revert the assassin reworks. Revert the MYMU. Revert the marksman reworks. Bring back the laser turrets. Go back to the old shutdown system. Buff relic shield. Nerf spellthief's edge. Remove the eye sightstone items. Remove redemption. Revert locket. Increase sightstone and ruby sightstone charges by 1. Change control wards back into pink wards and make them reveal invisibility again. Bring back green wards. Revert the trinket system. Bring back runeglaive. Brink back sated devourer. Increase jungle xp. Remove hunter's talisman. Make jungle enchantments cheaper. Remove the "ally minions get stronger if you are higher level than enemy" thing. Remove plants. Bring back smite buffs. Bring back poacher's knife and ranger's trailblazer. Remove tracker's knife.