I often read the recommendation to stick to one champion. Yes i agree it is good to have around 3 mains and maybe another 4 comfort picks.

But first you need to play a lot. I‘m a Shaco main. But he didn’t just carried me from since to platinum the first time, he taught me how to play the game. Before learning shaco i just walked to my enemies to fight no matter what. Shaco taught me to be patient, to weave in and outcof tesmfights and play around my cooldowns. He made me a better player.

Ammumu taught me that sometimes its worth to ult first to better apply your other spells.

Graves taught me good pathing.

Fiddlesticks taught me to play around vision

Shyvana taught me how to AA reset

Every champ forced me into a certain playstyle wich forced mr to improve a certain aspect of my game. All those skill Transfer to the other champs aswell, but i would not have learned them by one tricking right away.

To make this work you have to play the champs long enough to learn their playstyle and i still suggest to reduce your pool at one point to your core champions. But you will also learn how your teammates have to play as marksmen, casters, engagers, peeler, assassins etc. wich helps a lot as a jungler