Real talk tho, matchups are very important. A better player can lose to a worse one because of matchup knowledge(1 of the adv of low tiers, the other is u get jocked harder lol).
But just the same a better player using a low tier can win simple by being better, smash knowledge. Playing a better game, ie better spacing better decisions.
What generally makes a low tier a worse character is simply because they have less options overall. Low tiers often have fewer approaches, lower priority moves, or lack in speed or power.
High tiers just have the ability to be less predictable. Of course all of this is indicative to playstyles but the high tier characters seem to have many more visual differences.
Why can fox and falco be played well by being campy and aggressive or anything in between..
Any player can lose to any player with the right circumstances. Just overall, playing a higher tier character you have a higher % of not being disadvantaged when entering a fight.
Also, I saw dj nintendo beat a few good players at genesis. They werent all known players but they werent scrubs. Somehow that dude wrecks samus players.