The Pox archetype is still a great and viable, its mono-black Pox that's not...
Black on its own just doesn't have all the necessary tools.
B/W can work and has:
http://mtgtop8.com/event?e=14029&d=283246&f=LE.
But if you look at that list closely you'll find no
Sinkhole or
Cursed Scroll, cards that I think are pure durdle material.
Personally, I find B/G the most interesting:
http://mtgtop8.com/event?e=14378&d=285961&f=LE (my list from a League I 5-0'd).
B/G is a little more forgiving and allows for some durdling, but that's because of the virtual card advantage provided by
Life from the Loam,
Crop Rotation and
Entomb. Not to mention the threat of Stage/Depths combo.
Bloodghast is just pure gas.
Don't get me wrong, I'm constantly tweaking the list, but I never really feel completely out of it when it comes to match-ups..Sideboarding correctly is something I sometimes find very difficult, but getting better at...
For example, some of my tough match-ups is Shardless Bug. I usto keep
Hymn to Tourach in against and all my discard; until I realized the board was more important...esp since they can
Ancestral Vision.
Imho, Pox isn't supposed "to turn the corner", its supposed to back your opponent into one...
Just my two cents.