Why are there champions in LoL that are currently vastly outclassed by others? For example if Riven is available there's no reason to play Fiora. Why are some champions inherently stronger than others even if they are supposed to fill the same role? There are oplenty of other examples I'm sure you guys can think of where one champion beats the other one just counting on base stats better and useful ratios and so on. Is there a reason the game is designed in this way, where you can't play any champion but have to play the ones that are viable if you want to be an asset to your teammates?

No champ is useless you just need to know what does what and how, Mind you though every time they buff or nerf a champion they need to do something about every other champ too.

There are perfectly good reasons to play Fiora when Riven is available. Fiora has an uninterruptable AoE ult that leaves her immune - fantastic for cleanup work in an AoE team, which is a composition Riven does not shine in.

Every champion has their place, but some champions are easier to fit into team compositions than others.

Man speaks truth, i would fiora any day over riven. Super tiamat + ult = enemy team wondering what just killed 3 members and is killing the last 2.

That makes me want to try Fiora, Yasei.

I could show you how I build her if you like, Im not pro, but it works for me.

I have a pure AD rune page, because its funny.
Starting off with a Dorans, that = 110 Damage at the start.
I then get repostle first, 2 reasons. 1 it gives me + 15 damage making it 125 damage. and 2: Parry's the adc's auto attack.

My build finishes with these items.
Atk speed boots (HomeGaurd)
Super Tiamat
Blood Thirster
Infinity Edge
trinity force
Then what ever is nesasary

I believe a better example of a outclassed champion is Tristana, sure she's a hypercarry with long range but vayne also is hypercarry and has high damage output mid game, tristana not, also vayne has CC and properly played can kite and evade skillshots.

Tristana is far behind from Graves, Vayne, Caitlyn, Twitch, Ezreal, Draven, etc I believe tristana needs a rework, seriously look at his skills;

Rapid Fire (Q): Boring buff yet the most powerful skill in his skillset and the reason why trist is playable.

Rocket Jump(W): Very unreliable escape since while on air you can get hit by anything, still decent skill.

Explosive Shot(E): Useless skill vs champions no damage no range, troublesome at farming because push the lane, serously need a rework.

Buster shot(R): high damage at level 6 then is just a crappy knockback with high cd. By the way Vayne Condenm > tris Buster shoot.

Tristana has 0 mid game pressence, no utility, unreliable escape, useless skill(E), completely outclassed by many carry's.

Thats if u play her AD, all her skills but Q is ap, not to mention the jump bleed knock back combo v=can do over 3500 damage if you know what to do, but i do agree every other champ has made tris less viable.