I like the Smash Brothers series a lot, and I will also admit I'm not a competitive player. But I do know that I can win matches playing low tier characters in Sm4sh, even against somewhat competent online players pulling off fancy combos, tech-ing and generally being a better player who's probably put more hours into the game. In part it helps that Sm4sh more balanced than previous instalments, but in some ways I like to think it also comes down the ability to read the opponent.
Games that give the opportunity to read an opponent are great fun, since it lets you make up for shortcomings generally associated with a character or build deemed bad due to slowness and predictability. Smash Bros. is a great spectator sport because any action/reaction between fighters can be easily seen by the positions of the characters rather than just the health bar. This also means that you can easily spot habits being used by players without necessarily watching their characters every move. This is also probably why I personally don't play fighting games like Street Fighter as much - I am bad at technical skills.
As an example, my least favourite characters in Sm4sh is Diddy Kong, and my favourite is Ganondorf. Why? Because Diddy Kong is a super fast character built around chaining tonnes of attacks, grabs and other tomfoolery to rack up that damage and KO the opponent. Ganondorf, like the other heavyweights, just hits like a truck. I can sit and watch what my opponent is doing, pick up on their general play style, and then punch them in the face for massive damage - like a reverse Giant Enemy Crab. For me, this makes him all the more rewarding to play - win or lose (unfortunately Ganondorf has a bit of a bad habit of being a disrespect character but that's another story).
|Meet Abacus: stabber of knaves, praiser of suns.|
Of course having technical skill is great, but without game sense you're just flailing. Flailing impressively, but flailing nevertheless. Mental skill is a powerful asset if you know the concepts, but if you can't execute any of it you will lose with great haste. With both, you become a nigh unstoppable machine of doom, able to watch and respond appropriately to any situation (until someone better comes along). In fact, just go watch this video.