Then your mechanics are bad if they aren't trained and are inconsistent. The only way to get good mechanics is to have consistency. Mechanics definitely go hand in hand with game sense though so if your game sense to clear corners or absorb map information is inconsistent, this will partially affect your mechanical ability to move and aim accordingly.
Reyna is only ass in a professional level because she is the greedy agent. The vast majority of the player base say "pick Reyna" because she is the most self-sufficient agent if you are actually consistently good. Heal, dismiss, ult lets you go full-invisible when dismissing. It's just a fact that you can climb with really good aim and some map awareness. If Reyna is not available, players often pick Clove because of the temporary self-heal and self-res abilities. They're selfish agents that enable individual success because when you're in really low ELO, you cannot trust your teammates to do the right things a lot of the time.
If you're adamant about playing agents which can enable good coordination: Sova, Omen, Fade and Yoru are some of the best because you can set up the team but also set up yourself. Yoru is evidently the best agent in the game right now. You can play in so many ways with this agent that the only way you fail on this agent is if you don't use the abilities correctly or at all.