How is Sylas not just a standard problematic bruiser from 2014 and earlier?
Let's pull up a C L A S S I C red post about League's Bruiser/Fighter/Melee (later called diver) problem from the one and only Morello so long ago: http://forums.na.leagueoflegends.com/board/showthread.php?t=3608061&page=9#post44409164 I recommend reading the whole thing but I'll just pull out what I think of as the important bits
And oh, what a love letter it was. Xin was tough as a nail, bursty as an assassin and had chainable CC. Our solution was to try to give them everything we could to make up for the melee nature. While Xin's tuning was absurd on launch, the formula worked in the "here's how melee can be viable in LoL." The problem is that approach left us little we could do to adjust playbalance outside of power and numbers.
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The problem was that we didn't have nearly the sophistication with understanding what effect this would have on the game long-term. We'd all get different insights and peeks into it, but never anything to change course. It was really in the end of 2011 (after a very storied Volibear development) where we went "OK, what the **** is happening here."
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Now, we get into last year and up to today. Fighters have these problem more than even (Hi, Riven!) and they all live in a world where any of them that don't are completely useless. In the short-term, we try to play whack-a-mole to keep it in check somewhat, but it's a bit of a futile battle - as long asone champion has this problem, no others can show up with interesting stuff, meaningful weaknesses, or a laning phase that doesn't have everything.
My understanding is that the problem was that melee champions kept getting all the important skills to counteract being melee in spades and then... what else can you do? If the melee generalist is remotely viable then why pick anything else over him.
And Sylas seems to be this champion yet again, after Riot has spent years trying to refine melee champions into solid niches by saying juggernauts are always going to have trouble getting to targets and divers are just not going to get the burst required to pop a target, here comes Sylas to destroy all their hard work. When he gets in he's got great burst or he can slow his combo down for solid sustained damage, but if he can't get in he can still harass from a bit of range, he can AoE for waveclear, he deals extra turret damage and synergizes with the spellblade line to split push even faster, he's got cc (soft and hard), he's got mobility, he can shield himself to soak damage, and he can heal himself to sustain and stay out in lane (I'll get to his ult later). His early game's not bad, his mid game's really good, and his late game's pretty solid too. He's got the tools to survive against ranged targets, but they're all even better at bullying melee. He's got the damage to solo carry, but also the utility to help his team win when he's behind.
tl;dr he just seems pretty good at... everything...
And nothing captures that more than his ult. What's his ult? Whatever ult the enemy has, the ult of his choice, out of 5 ults it will be the ult he most wants/needs to use (or at 16 ALL of the ults he wants to use) and odds are the enemy will have at least one good ult. You're against him in lane: Is your ult really strong and you depend on it? Well he gets all that strength too. Is your ult just for utility so he can't get much done with it? Then that means you aren't getting much out of it either (or worse, your jungler shows up with a really good ult and Sylas gets to use THAT one). Instead of designing something to give Sylas a clear niche, Sylas has the most generically powerful ult in the game because it just does the best of the enemy's ults and there's no way the enemy is going to pick 5 champions with crappy ults that don't influence the game.
So what is Sylas supposed to look like when he's balanced? When should he be a good pick? When your team needs damage, or cc, or a brawler, or a split pusher, or an assassin? so... any time? When should he be a bad pick? When the enemy doesn't have ults? Because that sounds an awful lot like Sylas is forcing the enemy team to pick a really, really bad team comp.