Also ranged deals only 1/3rd of melee damage at nearly twice the price per part, so I'd say that balances it out pretty well.
Edit:
Also I wouldn't treat the damage as "reflected" per se. In RPG terms, this is more of an attack of opportunity hit/hitback, and as such depends on the part composition of the creep being hit, regardless of how much damage it gets hit for (as long as it survives the damage, i presume).
So if two creeps with ATTACK parts are hitting each other, they effectively deal twice the damage of their ATTACK parts to the other creep.
Which also makes the point that it's more cost-efficient to create fewer but bigger creeps than a lot of small ones, unless you're making ranged swarms.