Greenstone.Walker
Adventurer
An archer going up against a deadly threat can (and IME often does) poison his weapons:
That's not something I've ever seen in 2 years of 5E. Perhaps because none of the players in any of my games have taken the tool proficiency.
As for this thread, cantrips are there to remove the need for spellcasters to use crossbows. In 1E, it didn't feel very wizardly for you to cast your one magic missile and then spend the rest of the combat plinking away with a crossbow.
Unlike bows, cantrips do not run out of ammo and cannot be disarmed. They also do damage that is less resisted than nonmagical weapons.
As far as eldritch blast is concerned, it does the second best damage in the game, out to a range longer than the short range of every ranged weapon except one. With invocations, it adds ability score damage (admittedly, every ranged weapon already does this), it pushes the target back, and its range can be extended to well beyond the short range of every ranged weapon. Higher level Warlocks get extra attacks with it, so they can hammer one target or spread the damage out among many. It is by far the best damaging cantrip in the game.
On the other hand, an archer can fire inside a silence spell, which a warlock cannot.