Your party to me seems to be a rather weak one, but that may be personal taste, and connected to my denial to use any gadget (like bombs) instead of skills and because of my lacking knowledge of the Bard class. I would surely not compose my party so single target physical damage centric. But as the combat in the game is not very difficult, every party composition should work.
If you plan to be mostly ranged, replacing the Barbarian by a ranged class makes sense. You lose however at least 2/3 of the damage you had if you take a Hunter Ranger. That could change if the Sharpshooter feat is in the release, for which I hope. Compared to that, the decision between Colossus Slayer and Horde Breaker is not that important. I would choose Colossus Slayer because it is just reliable damage and helps against boss creatures and normal creatures.
Do you play with Karmic Dice enabled or disabled? If disabled, how do you get the Advantage you then need to be effective in combat? Can the Bard give Advantage to the Fighter and Ranger who are lacking here?
