Current state:
projectile_damage is the only way to improve arrow damage as characters level. This has the undesired effect of making Snowballs overpowered.
Future state:
Split arrow damage into it's own category similar to weapons and give configuration options accordingly; if possible allow the same method for multiple arrow types as well.
Example:
properties: [
arrow_damage_bonus: 3
]
"minecraft:arrow;damage=5"
minecraft:arrow;damage=11;model=Diamond Tipped Arrow"