Sweepers and Reds need to reveal clones
It removes all counterplay to have the clone not only able to body-block despite being an ILLUSION, but also have no possible way to distinguish it from the champion (considering that in close-quarters Shaco's E looks no different from his auto attacks). This isn't such an issue for Wukong or Leblanc, since their clones can't attack and don't last long. But since Shaco's clone actually deals a hefty amount of damage, applies on-hits, and lasts a while, having no counter to it is, quite frankly, unbalanced.
And such a strength with no counterplay or counter-build to it also creates difficulty in giving the character adjustments. Buffs can't be too impactful if he's doing poorly, because his kit has so many aspects to it that are designed not to have counterplay.
This used to be balanced in a way by the fact the clone didn't get jungle buffs when spawned, but they did away with that in season 5. But then it was still possible to quickly click both and check which had higher AD, since the clone would always have lower. But some time between the Assassin update and now, they removed that possibility as well.
