It isn't Talon. Coming from a Talon main (I love him so freakin much.
<3)
Assassins in general are good against low ELO players because assassins are designed to kill carries and snowball. Low ELO players don't tend to be as conscious of protecting their carries, and the tendency of low ELO players to go on tilt helps snowball-centric champions carry their way to victory in that kind of setting. A fed Assassin is a scary thing early and midgame, and unlike high level play, where teamwork is more important than individual 1v1 skill, lategame isn't as big a factor, so the fact that assassins fall off late (Looking at you, Leblegh) doesn't hurt them as much as it should. Also, Talon is about as close to balanced as a champ can get at this point, especially considering he's an assassin, which historically has been one of the hardest champ archetypes for Riot to keep balanced within the meta.
EDIT: I noticed a comment below where you mentioned that Zed needs champs low to kill them; keep in mind that Zed has a manaless poke on a very low cooldown that with shadows can be used from a long range. Talon's in contrast is a bit of a mana hog as abilities go, and it has a high cooldown until CDR comes into play. Less range by a good bit too. In other words, to even be viable with how little poke he has, Talon needs the CC and damage that his kit gives and that Zed's lacks. It's apples and oranges, and claiming that Talon is better or worse than Zed is silly. They're completely different champions with huge gaps in their respective playstyles. Hope my post helped shed some light. If it didn't, or I came off preachy, sorry.
Peace,
Flint Ironsides