Warlocks are really a 4th ed class. Think of them as teleporting lazer cannons. It's all eldritch blast all the time.

They were born out of the "I hate vancian casting" / why can't I wear light armor arguments around mages. If you only use a small handful of spells and tend to build "battlemages" you want a warlock.

Wyll comes set up for his story -- but once it's clear he's a warlock there's no reason for the armor and sword. Give him a robe and staff, take the mage armor and armor of something-cold-something spells and cast those as soon as you start out. He can't see in the dark so give him the dancing light amulet and have him cast it on the enemy before eldritch blast. Use misty step to get to high ground get advantage and away from enemies. If you can't get away from enemies use the arms of hadar spell.