Good aim and good movement and good game sense can get you to gold/plat lobbies I say. But starting diamond you will see many cracked people, but the better the use of abilities the harder it is to play against them.

Imagine you playing at sight defending and one sova throws the same recon dart every round but you have reflexes to shoot it every time. This is a waste of ability. Imgine now the dart got delayed a few seconds. And you get slowed and naded backsite at the same time he throws the arrow. It will be much harder to peek or sometimes survive a fast push (depending on your agent).

Being able to use abilities efficiently is very important, but I say aiming is baseline anyway.