Leagues "Secrets"

SO i don't fucking understand this one single bit.

IF for example i am playing jinx, and i get an infinity edge, i should be able to do the EXACT SAME DAMAGE AS THE OTHER JINX WITH NOTHING BUT AN INFINITY EDGE RIGHT? WRONG. Iv'e tried it out, and tested it.

I have full AD runes, like your supposed to, and yet not only does the other jinx have more range WITHOUT a rapidfire cannon, but she has more damage too? With the same items? IF THAT, ive been in matches where i built the full item sooner, and they did more damage with autos with a non full built item than i do with the full built. Okay, that makes sense, something fishy about that.

Same thing goes with tanks, how come whenever i get a tank, and i build tanky as fuck, i still die in 2 hits, BUT when the enemy team tank doesn't even build tanky, they build something like a black cleaver, they become unkillable? no matter what our team has, ignite, grievous, arm pen, huge burst AP people, it doesn't matter, somehow their black cleaver is apparently every tank item in the game.

Is this game really to the point of where even if u have the exact items, one team will still have secret buffs that magically make them do more damage, and survive more, and run faster? Seriously.

This game has so much underground shit, like ill never understand how i can have more movement speed than someone, have full boots, and they will outrun me without full boots OR ANY SPEED ABILITIES OR ANYTHING! how the fuck is that possible?!?! Seriously....

And yet all people will say is i suck, like okay, i'm sorry there's underground shit making the other team do more magical damage and run faster and have more range? i cant help it if i have the same exact items as someone, on the same champ, and when we both exchange 1 single auto attack, mine do 100 and theirs do 300, like honestly, that's not my fucking fault, i cant just click them a certain way to do more damage.

But yeah, i just suck, that's why i magically cant do the same amount of damage with the same attack and same items as the mirror me. That totally explains why if we both auto eachother at the same time, mine will do 100, and theirs will do 300.

I can literally prove it, try it yourself, get a friend to play the same exact champion you are in a private match, build the exact same item, have the same runes and mastery's, and auto eachother once exchanging blows, I GUARANTEE YOU, one of you will do more damage than the other, i can guarantee it, iv'e tried it time and time again. One of you will also have slightly better range, and movement speed.

Once again, skill doesn't magically make your abilities do more damage in an equal setting, it's all those secret buffs league has, to make certain teams win. How can a game be competitive when half of it is decided by secret buffs?