What that guy said.
I one trick Ryze a fuck ton. But that doesn't mean that I can't play things like LB, Malz, Syndra, Viktor, Brand, etc.
In fact, I play Ryze because I know him into every single match up, and I have the other champions as back up.
Given I can play Malzahar into every match up as well, but it is no where near as satisfying.
I also have a variety for plenty of different reasons.
1: For champions that Ryze and Malz struggle with. (Notably LB and Syndra fights) Not that they actually struggle, but I just really fucking enjoy that skill match up. Its the first person to fuck up that loses and hard.
2: Ryze and Malz can't deal with long ranged champions like Xerath, Lux, Ziggs very well. So I can also play LB Syndra, Viktor into those. But they are very situational. Certain conditions have to be met for me to play them. (Early game play style on the enemy part, something like Cait/Draven, Ziggs/Lux, Kha/Shaco/Lee, etc. IS LB or Syndra.) Mid game is Viktor when against long range. Late game is Ryze/Malz.
3: I dunno, the chances of a one trick getting banned is pretty low. Unless they are playing Zed/Yas/Akali/Irelia/Meta. There are 145? champions in the game. Assuming that every game has at least 2 useless bans (Aka a Yas/ a copy of the other side) the chance of someone that doesn't play high ban rate champions/meta is extremely low. I've seen Ryze Picked more often than he is banned.
Now to talk about the little bit at the end.
Iron/Bronze/Silver aren't competent at the game. Lets get that out of the way, sorry guys. You just aren't. There are still a bunch of things that you don't understand about just the game. Some of you are great at your champions but really really suck at understanding the things to do.
At gold is when you can say people start getting somewhat competent. And even then its a long shot.
At plat is when people start becoming a recognizable level of competent. But at that rating, they are normally able to branch off to similar champions with very very very little practice. For example, I played a fuck ton of ryze, and when he was getting banned back in s7, I picked up cass in like 3 games and did well with her. Similar champions are things that you can play. Hence why assassin players play assassins. Mages other types of mages, adc's with adc's. Because the core game mechanics stay the same, the interactions are exteremly similar.
What it sounds like to me is that you are talking bottom of the rung one tricks. And if that is the case, then lets talk about bottom of the rung no tricks. The ones that just play what they want, and don't have a full understanding of any champion. Full understanding being how every single match up goes.
I'll use a friend of mine. He watched me play into a Fizz and absolutely fucked him, he had 30 CS at 10 minutes. And wanted to know how to do it, and I explained it to him. He couldn't reproduce it because he doesn't understand the ranges of his own champion vs fizzs. He misses windows of opportunity for harass. And he chooses bad times to harass.
And he is a plat player. Meaning that he has a very good understanding of what to do in the game, but can't perform in terms of mechanics.