The problem is that Eve is an assassin and Twitch is an AoE DPS. Shaco is more or less a non-issue, because if he does it right he won't be seen until it's too late anyway (built in blink).
Eve being an assassin means she can deal very very large amounts of damage in short periods of time, but she can't even take half of what she can dish out most of the time. This is the nature of being an assassin. The fact that she is a stealth champion just makes it worse, because that kind of sustained burst on something that can go invisible is terrifying. So she is even squishier than other assassins. Her double squishyness makes her completely reliant on her stealth to do anything at all, and even then she is not safe from rogue skill shots and AoE's that can kill her before she even makes her move. This is further compounded by the fact that she is a melee champion. Melee champions have to get up close and personal to do anything. In this regard she gets gimped by Oracles more so than Twitch, since she has to run in and attack you at the center of your reveal radius to hurt you.
Twitch is probably the most unique class of DPS. He deals sustained AoE physical burst, and a lot of it. He also fits into the assassin class, meaning he is squishier than his own damage potential. This squishyness makes him reliant on his stealth to get into position and hide until the time is right to Spray'n'Pray the entire enemy team, though not as bad as Eve, since he is ranged. His range, in fact, is about the same as the Oracle reveal radius. So even if you do counter him, it's a gamble to whether or not he will be seen.
Now to the general case. Stealth is a tricky mechanic to balance. But I think we can all agree that if all champions had a natural "true sight", it would defeat the purpose of even having stealth champions at all. It would in fact destabilize them further.