I'd have to agree.
When it comes to a future shock, I'd presume they're really hard. You have to misdirect the audience so they don't see the twist before the last panel. However, in five/six pages, the reader is essentially "looking" (even if unconsciously) for the twist. It's tough gig, so I salute anyone who makes even a vague stab at it.
Revision after revision after revision to tighten it up and remove flab can sometimes mean you're unable to actually "read" it as if you're coming to it fresh as your reader will be. Not brilliant, but not bad by any means. Keep at it mate, we're all quite happy to offer any assistance we can.
Keep at it, ok? Good stuff, but I can see why Tharg didn't pick it up. Treat it as a learning experience and you'll improve as a result.