Why is Shaco being nerfed?

In order to make Shaco work well, Shaco players had to build AP with three items that allowed him to deal enough burst to actually kill someone. Echoes, Gunblade, and Lich Bane. Without those items, AP Shaco would be hard-pressed to kill anyone at all. His current burst damage ratio is:

90% from E 50% from Q 20% from Backstab Q

Which is a grant total of 160%, 140% without the backstab. These are perfectly normal AP ratios for an assassin champion.

Riot wants to nerf that to

75% from E 40% from Q 18% from Backstab Q

Which is a grand total of 132% with Backstab, 115% without.

115%. That's almost less than pre-rework Shaco's E did (except that spell actually had a base damage of more than 5-125)

To compare, here are the ratios of some other assassin characters:

Fizz's is 143.3% with QWE, 243% if they've been bleeding two seconds prior (Q, E, W proc will do the trick) LeBlanc's is 160% with QWE. No passive procs Akali's is 210% with QER, Ekko's is 210% with QE with passive Diana's is 250% QRWR

Shaco's position as an assassin that can play AD or AP is a unique one and one that I think should stay put. It gives Shaco a nice niche to play into. AD Shaco builds virtually no AP and AP Shaco builds virtually no AD. AD Shaco is is an OK spot. Not the best, but OK. AP Shaco is in a spot where he can reliably do his job after building all the items he needs to, which is what Riot had intended originally. A weak early-game, a decent mid-game, and a strong late-game. Nerfing Shaco's AP ratios to such an extent with no compensation is going to destroy his ability to keep up with any other AP assassins and he's already struggling to keep up with a lot of the AD ones. To the point where lots of Shaco's just build bruiser and play as an off-tank with damage.

So I'm curious: Why are we nerfing Shaco? Why are we trying to keep him from doing his job as an assassin? Why are we trying to force him out of his AP role? If you need to nerf him, nerf him in small increments or nerf the items that he, and other champions build all the time to increase their burst damage. Lich Bane, Gunblade? Those are the things that make AP Shaco so strong and what make Akali and Fizz so strong. He's nothing without those items and the other champions that use those items use them just as well as he does. Look at the items, then look at Shaco, and if you choose to nerf him, make sure that you don't remove his ability to kill people as an AP assassin, because right now that's exactly what's starting to happen.

@Riot @Meddler