As per usual NA didn't look to hot this year, even teams like Splyce (EUW third seed) went further than NA's best.
I'm going to speculate why NA keeps under-performing every year by looking at C9 Sneaky. This is not to point finger at him, the issues with Sneaky are similar to the issues that applies to most NA pro players.
**1) Work ethics are super low**
After loosing in worlds Sneaky took a vacation in Korea.
Sneaky also went traveling in the middle of the LCS season to take new photos of himself that he could later post at twitter and such. Mostly for "meme points" I suspect.
We could also track sneaky during his time at EUW and he did not play a lot of solo Q. He never reached a "top rank" and korean/chinese pros that arrived later surpassed him in both games played and rank sort of quickly. 10 hours solo Q is nothing, the Koreans/chinese pros were online for so many more hours 16-20+ hours days daily are common and they scrimmed too. The dedication to the game also assured they stay in the tournament while Sneaky and his team went packing.
**2) NA pro's suck because Riot is treating them too well**
After another year of failure Riot is again pointing the finger at themselves asking: "What can we do to help NA so they don't suck?"
We hear ideas like low-ping servers, more tournaments, more scouting to find new talents and what not. But I think the main issue here is the pro's themselves.
NA pro's think they can relax, travel, stream etc for 10-11 months of the year and then when it's time for worlds "get serious" and bootcamp for 3 weeks and catch up to everyone else.
It just don't work that way, hard work triumphs everything and other servers are putting in hard work. You are never winning or even getting close to winning worlds unless you have a team of players that are willing to put in more time than a normal 9to5. If NA want's to compete and be among the best they need to push it's players to practice as hard as Korean and be willing to spend at least 14-16 hours days most of the days perfecting various aspects of their game, you can count in time spent at the gym as practice.
**3) The lack of competition is enabling low work ethics**
Take a player like Bjergsen, he know there is basically nobody in NA that can take his spot. He don't have to work hard in NA to stay on a team, in EUW or Korea he would have been replaced by now after the lack of success against C tier teams, but he still stomps or do OK against most NA mid-laners.
Take sneaky, the guy suffer from low APM. Yet he is the best option C9 have (when you consider fame a plus). He looks "okay-ish" in LCS but he lose lane every time when he faces a competent LPL/LCK/LEC team. Yet I'm 100% sure he will have a team in NA next year as well, and he won't be preforming any better, Sneaky just like most NA pros don't need to be better than he currently are to stay in a top team in NA.
**4) NA don't hire to win**
Overall you can just check the roaster of most NA teams and know you won't win, you know it, everyone knows it. But perhaps "winning" isn't even the goal of NA teams, you don't employ say sneaky due to his "mad skills".
You hire him due to celebrity status. And you want the exposure he gives to your brand.
NA need to value "skill" over "celebrity status" if it are to compete and not be a meme at worlds. But I don't think this is changing, NA loves it's pros and NA will probably disappoint next year as well due to this and various other factors.