First off, let me preface this by saying maining a champion and playing said champion every single game is, in my opinion, a terrible, horrible idea and will not work. Sure, you might perform better on a specific champion and learn to master a specific champion, but for the purposes of advancing, you should base your pick around what your team needs, and what counters the enemy team.

Reading the rest of the guide, you seem to have a good idea of what you are talking about, but the above is just wrong.

Most players in the lower brackets are simply incapable of successfully playing outside of a very small champion pool (2-3 champs at most).

Team composition really does not matter much in the clownfiesta that is Gold and below. The most important thing is that you're not hard-countered in your lane, but even that has fairly low impact, because matches usually go into the late game, giving you a lot of time to recover from a lost laning phase.

There are so many things to worry about during a match that you really want to be able to play your champion on autopilot, so you will have enough cognitive capacity to pay attention to the map.

Furthermore, for each additional champion you play you will have to learn the counters and counterplay as well. It's a lot easier to main one or two champions and have a good idea of all the possible matchups you are going to face.

People like Dyrus strongly agree with that, I've seen Dyrus say repeatedly on stream that he much prefers to have a one-trick in his team over a two-trick, and he wasn't even going into people playing 73 different champions...

Being a one-trick is only bad if that champion has a high ban-rate or is hard-countered by a lot of different meta champions -- but in that case your win rate will probably be low anyway and you will soon notice that it's probably better to play a different champion.

Your Shaco remarks were brutal ;(
Nice post though