Okay, well if you have 18 CHA and 18 STR, then of course not. But why are you building STR on a Warlock? You already need high CHA for casting, and solid DEX and CON for durability and saves.

2d6 is an average increase in damage over 1d10 of 1.5. Yes, the +1 to the greatsword helps this, but again, why in the world is your STR so high, and what do your DEX/CON scores look like in exchange? WIS too, that's an important save and the Perception skill is very useful. Insight for a CHA character can also be helpful.

That Greatsword also only deals that increase in damage (about 3 more damage per attack when you factor in accuracy? Yea, that's pretty solid) from melee, and considering your STR and CHA are both at +4, I doubt you're durable enough to stay in melee for long. EB can hit from hundreds of feet away with a few modifications. Without Darkness, of course, and I assume you also have either Dark Vision or Devil's sight.

So every combat, you're popping at least 1 slot for Darkness (or 2 for Darkness then Armor of Agythys or Hex), in order to deal some more damage in melee...because you have a +1 version of the hardest hitting weapon in the game. Or, you know, you could put that 18 into a useful score like DEX or CON, and deal almost as much damage, from really far away, without needing to blow a spell slot every fight.

Also, you're GS damage caps with 2 attacks, where as EB gets up to 4 beams. 4d10+20 is really pretty for a cantrip.