Duskblade has a lot of stuff going on for it.
2900 gold, so it's relatively cheap.
55 AD
10% cdr
18 Lethality
A passive that can be applied multiple times in a fight, applies a 99% slow (no matter how short the duration, that is still very strong and annoying to play against), and does extra damage.
Blackout. Free sweeper every 90 seconds that you don't even have to think about activating.
I don't understand the thinking behind the slow, at all. The people that are building it don't need it.
etc. They don't have issues keeping up with people, they're already mobile and they already have CC.
just a few example to show u what's they face with high mobility.