Alchemist
Remove transcendence from the game, cap anvil enhancement at +15 and make Briquetting and Awakening the most relevant ways to enhance weapons and armors. Using Blessing Gems as sacrificial materials for an Awakening should add unique possible results like AoE Attack Ratio and +1 to X skill, for example.
Hunter
Fix pet AI, remove pet stamina system (pet food should buff your pet instead) and make Coursing work against bosses with the debuff values halved.
Scout
Replace Perspective Distortion with an active buff that increases the party’s Missile Damage. Rework Scan, make it a skill that places a ward that will detect hidden enemies and items in the area around it. Remove Split Arrow overheats, but add a self-debuff that increases its SP cost by 50% every time you use it (Max: 10 stacks, 5s duration).
Shinobi
Rework the whole class. It was balanced before the combat rework patch from May, but now its very concept is simply broken. Nerfing Bunshin no Jutsu would just turn it into an useless class, so replace Mijin no Jutsu with an actual useful skill, buff Katon no Jutsu, fix Mokuton no Jutsu clunkyness and rework Bunshin no Jutsu.
Rune Caster
Reduce casting time of offensive skills from 3 to 2 seconds (1 second casting time with Quick Cast maxed then) and rework Rune of Giants FOR GOD’s SAKE. Give it unique skills like Lycanthropy and a native Pain Barrier effect.
Archer
Make Heavy Shot compatible with muskets. Allow the use of all missile skills while in Kneeling Shot status (Fletcher, Mergen, Musketeer, Ranger, etc.).
Fletcher
Give it some synergy with Mergen, e.g., attributes that enhance Mergen skills with Fletcher arrows.
Ranger
How about making this class more interesting? Remove High Anchoring charging time, buff Critical Arrow and Time Bomb Arrow, give Ranger3 an attribute that gives Steady Aim 100% uptime.
Barbarian
Increase Seism and Pouncing scaling. Make Stomping Kick work like Hoplite’s Long Stride (select the area and your character will perform a jump in that direction) and give it an attribute to increase its AoE Attack Ratio. Make “Frenzy: Maintain Stacks” (Barbarian C3) attribute remove all Frenzy restrictions instead of cutting stacks by half when you attack another target.
Wugushi
Replace Bewitch with a small nuke that deals damage to poisoned enemies around you (with an attribute to apply Confusion like current Bewitch), like LoL Twitch’s Expunge/Contaminate. This skill now is maxed at level 15. Also give it an attribute to increase Wugushi poisons duration (Wugushi circle 3 required). Make Detoxify a max level 1 skill. Give it an attribute to neutralize poisons of any level (Wugushi circle 2 required) and another attribute to also remove Bleeding, Stun, Shock and Slow (Wugushi circle 3 required). Rework Zhendu and make it work like Enchant Fire (extra poison damage line based on your weapon’s minimum attack and additional poison property damage based on your STR and DEX).
Too much wishful thinking, I know. But that would make all underplayed classes competitive again.