Dark Harvest Shaco is kinda sorta cancer (when it works)
Now hear me out...
I get that he's gotta stack that shit up. I get that it takes time, an has a failure scenario. I get that its risk/reward. I get that he's glass cannon squishy. I get that he can be counterplayed by good vision control. I get that it takes some skill to make it work.
I fully understand that the success condition for this is a very, VERY narrow window. I do.
So now that we've got all that out of the way..... HOLY SHIT.
When it works, its fucking impossible to deal with. He can literally 1-shot anyone. And he can do it in quick succession. Hide, Q in, delete someone, run away. Q over a different wall, 1-shot another person, go run and hide again. Q in, delete someone, go hide again or clone or whatever. In a matter of seconds, your whole team is dead - all from shaco, and all with almost ZERO time to react.
It is 100-0 before you can even react with duskblade + IE + shiv. Like he shows up and you're just dead. 100-0. Zero reaction time. One auto attack. Boom. You're dead. Don't even know what hit you (well you do... but figure of speech)
Just because there's a lot of failure conditions for the playstyle doesn't make it any less horrible to play against when it DOES work. Especially if you're an adc or mid laner, or non-tanky support. And even tanky champs are probably flashing red, and there's 4 other members that still haven't even started putting their damage out.
You can just be walking out into a lane, and before you even get out of your base, all of a sudden there's a shaco and a small explosion of blood and guts where your champion used to be. And all he did was auto you ONCE. From invisibility!
Anyone here ever play Perfect Dark? back in the day, on N64? Shaco is a farsight rifle shot to the head. There's literally nothing you can do, and you never see it coming.
That SUCKS to play against. Your best option at victory is to press /ff and try to win the next game and pretend it was this one while you sob softly into your headset.
TL;DR - Despite its narrow success condition, when this playstyle DOES work, it is impossible to play against, extremely unfun, and basically forces you to forfeit the game, unless you just like dying over and over and over.