Scout is OP in easy mode games, and games where he can just solo farm with no pressure early.
I was playing last night vs a team including madman and scout and we ripped them up because while scout could periodically remove half your health bar, he couldn't farm in the lane vs myself as thunderbringer in mid or the crystal maiden babysitting our (terrible) night beast in bottom, and a lane of madman + scout in top would be hilariously bad.
As a result he could leech xps, but wasn't get last hits, was undergeared in the end game and got ripped up as a result. If you want to beat scout, you need early pressure and a non easy mode game.
the wards skill makes his ulti very useful. you can just put a ward behind them in their lane (obviously not next to tower though) and then when they are out of your sight, the ward will clear the fog.
random example: if you are pushing mid and you put a ward half way up their lane, chances are you will get them somewhat low and they will go back. then you can start channeling your ulti and they will go straight back toward your ward nine times out of ten and you will be able to see them with the ward.
Scout is horribly weak for competitive play. His potential for pub stomping even in weak hands means he should probably stay as he is, though. The game isn't well served by having heroes that dominate low level games.
Compare it to how Clinkz has been kept underpowered for ages in DotA.