Phoenix is a W first beginning agent. Has all the fundamentals for a lot of agents. Has flashes, heals, molly, wall, and a ult that recharges quick and u can run it down.
But what player is going to practice just aim until their aim is decent enough, and then play? New players are just going to pick an agent and start playing probably long before they get a grasp on how to aim. Reyna is literally the smurf agent for a reason, because it's about how much better at aiming you are than the enemies. She's not good for someone new, because figuring out how to use utility to benefit your team is often times easier than learning how to aim well.
I would prefer a player who doesn't fully understand how to use their util over a player who is on YT guides looking at util videos and is incapable of aiming.
100% it is easier to climb when you're better at aiming than when you're good at using util.
So why not play an agent which eliminates the need for the less useful skill so you can focus on the more useful one