Since it came out. I too, played almost every day after high school with my buddies who were also gamers and into Smash. Still play it (not as often), love it, and am still the best of my little group of nobodies much like yourself. You don't need to tell me how to play, or how to win with mid-low tier characters. I don't even play high tiers... Roy, Kirby, Luigi. I can win just fine. My point is that it doesn't mean that someone playing a higher tier character doesn't have a *base advantage* over me. If my own skill vs. theirs overrides the advantage then I still win, obviously, but that's not what *balanced characters* is about. The fact is that if you knew how to play all characters with 100% efficiency, your Fox would beat your Falco, your Falco would beat your Luigi, your Luigi would beat your Pichu, etc. The developers (understandably) were not able to give everyone the same advantages in ability. Some characters are simply -less able- than others, and because of this they lose those options and strengths, and they are ranked lower on the tier list. Nobody is saying that Yoshi can never, ever, ever beat Marth or something. However, in a high-level match the Yoshi player would have to be *significantly* better than the Marth user in order to win.
Go play in a real tournament against a Marth/Sheik/Fox player who can wavedash, shffl, L-cancel and all of that pro jargon, and you will not just get damaged, you'll probably get it handed to you. I'm sure you're good and everything but there's a whole wide world of monsters out there, and trust me when I say the information presented here in this thread is straight *from them.* Just looking at your analysis of Sheik I can tell how isolated your knowledge of this game is. 3/4 of Sheik's air As are deadly as hell and she has some of the most ridiculous combos in the game if you know them. There's a reason pros choose Sheik, and there's a reason that tier list exists.
Tiers are a harsh reality.