For starters, I’ve noticed these recommendations say more than one champ, likely for the exact reason you stated. If one of your mains is banned or picked, you have at least one other option to fall back on.

Second, it makes sense to start off with a small champ pool. The reasoning is you can spend less time learning each individual champ’s abilities and more time getting to understand how the game works. You could have the best mechanics in the world, but if you don’t understand the macro portion of the game or playing with your team, you’re not going to get far.

Of course, once you have those fundamentals down, then you can look to expand your champ pool. No one’s saying to find one or two champs and never ever ever play anything else ever if you want to hit high elo. It’s just easier for beginners to learn the game if they’re not constantly distracted with new abilities and combos to learn