I would keep a hand that looked like this in a heartbeat:

LED
LED
Street Wraith
Faithless Looting
Golgari Grave-Troll
Golgari Thug
Careful Study

No question. That's an incredibly powerful turn one play that can open the door to some seriously broken shit, especially if you're on the play. It's a far more attractive hand than replacing the Street Wraith with Breakthrough in that scenario.

Breakthrough is def. the worst spell for G2 and will usually be cut to a certain extend for g2 in a lot of matchups, however there are also a good amount of matchups where you'll need it ( DDft, ANT, TES, Maverick ( considering that we don't sideboard against them and just try to outrace Ooze / KotR / GSZ), etc.).
Street Wraith can be used for free at any time. That means if your turn one play is Careful Study, draw a Street Wraith and discard some dredgers, you're getting more action for free immediately - and will be able to feed a potentially dredged Ichorid in the event one is binned off the 'Wraith activation-into-dredge. I'm simply saying that the issue with Ichorid is generally in the slower games being far more relevant when you need to have black creatures other than your dredgers to recur them into play.

I am not totally cutting Breakthrough. I still run two in there.

And using Breakthrough as a turn 1 discardoutlet isn't the worst thing you can do ( if you mulligan into oblivion).
Assuming you absolutely find yourself mulling into oblivion, casting Breakthrough is fine. I even defeated A.J. Sacher under the exact same set of circumstances at the Open in D.C. earlier this year, where I mulled low and just went all-in on a Breakthrough. It paid off, but the fact is under most circumstances you're wanting a draw spell or discard outlet instead of Breakthrough - which should get boarded out in the appropriate match-ups.

I am not running the Quadlazer list, for reference. I think you have that confused with the traditional LED Dredge that I opt to run. The lists are comparable in a general sense but quantity is what the Quadlazer list is highly predicated on, maxing out on four-of's all across the board.

I'll be playing this list tomorrow at the local. Updates then.