First the #1 common factor in top level smashers is their determination to improve. We are not a very big community, our upper echelons are made out of people who got their through constant practice and study. We do have talented individuals as well, but "talented" players are not the only ones allowed into the top 8 at nationals club. The thing is, this is a fighting game who's meta has evolved over 10 years. If you local scene is older than a year, odds are that you won't be making bracket consistently in less than 2 years of time (Unless you pick some of the more forgiving characters).
You are having the same problem a lot of smasher's face at that point in time( and it won't stop there). You have spent more time and active effort getting better at this game, but your results don't reflect it. In the same amount of time you could be the high ranks in starcraft, or lol or dota with that kind of dedication. Even other fighting games such as SF 4 or MVC 3 would see you making bracket at least at locals and regionals. These games have more fresh blood for you to beat down than smash does, which inflates standing.
Think of it this way. When you are facing someone in pools who regularly makes bracket in an active, you are facing a younger games equivalent of a pro level player with probably 2 years or more competitive experience under their belt.
So I am going to put this bluntly. You are good enough if you can hold that motivation. If you can't, that's fine too, you are still better than 99.99999% percent of the world at playing smash. You'll whoop casual players. If that's not good enough then there is your motivation.
Sometimes you need to keep it fresh. Keep looking for new tech skill to learn, work on your platform movement(wavelanding rapidly to get around a level is actually a pretty fun and relaxing practice routine and will boost your movement by huge amounts). Learn a new character or play some Project M. Whatch top level matches or your favorite combo videos. And some times take a break and play some other games for a bit. You'll be jonesing for melee again soon enough.
On the matter of concentration you are not special. Lots of players struggle with this. Lot's of top players struggle with this. Playing this game and thinking about what your opponent has in store for you next is exhausting. Learning to think about this game while playing it takes more practice than any bit of tech skill you will ever pick up.
Also when you do think while playing, how much of it is about you instead of you opponent? If it's gravitating towards you and what you are doing or trying to do next then you are not comfortable enough with your character yet. Which isn't a bad thing if you have only been playing competitively for a year. Fully controlling your character takes longer the more technical you wish to become(And being technical is a good thing). Hell, it takes years for a fox player to have a good enough handle on him to actually start playing their opponent rather than just practicing tech skill on a human target.
Here is a little thought experiment. Pick shiek and only grab, tilt, shield and down smash during a match. Try thinking about what your opponent is going to do while playing like this. Focus on it. You'll probably lose, but I guarantee you will find thinking about this game a lot easier for that match. It takes a lot of real match experience to be so comfortable with your own toolset that you don't need to focus on it during a high pressure match.
Also the best way to keep the energy you need to focus is to have fun. Frustration will drain it away and you will get more frustrated as you lose focus. Which sucks, because many people (myself included) have a hard time detaching themselves when they are not doing well at something they are working very hard on improving. Learning to let go of that failure frustration is the hardest barrier to overcome. It will take a lot of active effort to avoid that line of thinking, but it's worth it.
Hope this helps
