League of Legends (LoL) Question: One role/one champ vs. all lanes/many champs?

What are you aiming to do? That's the most important question.

If you're looking to play as a team, playing multiple roles with multiple champions helps.

If you're looking to greatly improve, playing one champion / role helps a lot in learning how the game works because you eventually get used to the champ enough to play well with it as second nature, letting you focus more on the game flow, trends, etc.

I'm always pro-onechamponly because you don't really have a strong foundation with individual champion abilities and mechanics when filling.
Playing one champ / role only helps you to understand your role a lot better too.

being good at multiple roles is better for soloq, being great at one role is better for teamplay.

I'd say be good at one champ who can fill multiple roles, like a top lane/jungler or mid lane/support. Then have three more champions to back up in other roles that you can at least land the skill shots on, even if you can't play them creatively.

If I talked about my personal experience,I believe it is better to skilled in one role then having ordinary value in all the roles. Playing with one champ and role assist you a lot as continuously using same champ let you focus on game and its stream.

I suggest learning three different style champs that are not frequently banned in each role.

I will explain what I mean in an example. Let's say the enemy team picks Jax as their top laner, a very strong pick against auto-attack reliant champions. If you only knew to play melee carries like Fiora, Tryndamere, and Aatrox, you would have a difficult time in this match-up. However, if you learn three different style champs like maybe if you learned Aatrox, Jayce, and Ryze then you would still have two relatively strong picks against Jax to fall back on.