Padding ability scores like that doesn't do much. The best damage dealers are martials, specifically as melee. This is due to some unfortunate bugs in damage calculations.

- Off-hand weapons apply Str/Dex mod in damage, but not hit chance.

- Colossus Slayer works on full HP targets.

- Hunter's Mark stops Colossus Slaying from working the turn it is applied.

- Hunter's Mark triggers per damage calculation for melee.

- Great Weapon Master triggers per damage calculation; sneak attack, hunter's mark, etc.

- Opportunity attacks use both weapon attack if dual-wielding.

1. Ranger + Hunter (Colossus Slayer) + Hunter's Mark + Great Weapon Master.Get 16 Strength, or buy x3 Potion of Hill Giant Strength from Auntie Ethel every day.Get Light of Creation, then Whispering Promise and/or Ritual Dagger for bless.= 1d10+1+5+10+1d6 (slashing)| 1d8+10+1d6 (slashing)| 1d6+10+1d6 (electric)That's 60 damage on average if you hit. Unsure how GWF would interact.Bonus if you get the "wet" status, since it doubles the electric damage (2d6+20+2d6).

2. Rogue + Thief + Sneak Attack + (optional) Dual Wielder.Get 16 Strength, or buy x3 Potion of Hill Giant Strength from Auntie Ethel every day.Get Dragon's Grasp (off-hand), then Sickle from Redcaps or lit Torch, combine with poison.= 1d6+5+2d4 (+1d4) (slashing/fire) | 2d6 (sneak)| 3d4+5 (slashing) | 3d4+5 (slashing)That's 48 damage on average if you hit all three attacks.With the dual-wielder feat you can use Shattered Flail to heal every die roll.

3. Fighter + Battle Master + Menacing Strike + (optional) Dual Wielder.Get 16 Strength, or buy x3 Potion of Hill Giant Strength from Auntie Ethel every day.Get Dragon's Grasp (off-hand), then Sickle from Redcaps or lit Torch, combine with poison.= 1d6+5+1d8+2d4 (+1d4) (slashing/fire) | 3d4+5 (slashing)That's 33 damage on average if you hit the attacks.If they fail the saving through against fear, you get to do the attack again.Which is 61.5 damage, and the enemy is wasting their turn.

Honorable mention to Wizard doing Magic Missile + Sapphire Spark, for 8d4+4 for a 100% 24 damage on average, and Scorching Ray + Hex (Warlock Initiate) for 9d6 for 31.5 damage on average.