I'm playing a lvl 14 Fiend Patron Pact blade tome warlock and it is one of the most enjoyable characters I've ever played in D&D, any edition. He can hold his own in melee, but against a truly tough foe he's got to think it out. Close quarters? Darkness, which i can see through and most other melee classes can't, I win. Not close quarter? Charm the fighter into getting somehwhere I can use that combo. Or just make him my monkey for the duration. Invisibility, check. Ranged attack if needed, check. Disguise self to sneak into somewhere, check. He's got a lot more options out of combat, like rituas and guidance. and plenty in combat to help him get advantages when needed. All else fails, dimension door to get out of a bad situation and strike again when terms are more to my liking or that of my group.