Just picked up Zen again recently and here are some additional thoughts I had to add:
Zen’s balls are projectiles that have no drop off so they deal full damage regardless of range. Furthermore, he has the ability to charge his attack before unleashing it in a single burst. This makes Zen very good for stationary or slow moving targets such as Tanks, Bastion or Snipers.
If your team has problems dealing with a Torb turret or a Bastion, your priority as Zen is to shut them down. You can do this by hiding behind a corner to avoid the turret or Bastion targeting/seeing you and then unleashing the attack when you’re ready.
Against Bastion, try and discord the Bastion if possible before you charge your attack however that might alert them to your presence so it really depends on the situation and if you think it’s safe to do so. Once you’ve unleashed your first volley, they will either turn to attack you, ignore you or return back to the mobile recon form to retreat and heal. If he attacks you, retreat and duck around a corner and use your charge volley. If he moves to his mobile form or ignores you keep firing!
Against a turret, you can’t Discord it but it only has 250HP so a full burst volley should knock most health off and one more attack will destroy it. Most Torbs will be sticking aroudd their turret so you should try and discord the Torb after destroying the turret and start focusing him down.
Against snipers like Ashe and Widow, your best chance is a full burst volley from around a corner or behind a friendly barrier. You have a large hitbox so the key is patience or catching them by surprise with a burst to terminate them before they can retaliate.
Against Tanks, your key targets are Tanks that do not have reliable barriers. Roadhog is an especially good target as he has no self protection except for his ‘Take a breather’. This means you can reliable farm him for ultimate charge. D.va is in the same situation as her Defense Matrix is only temporary however she can reliable escape or chase you down with her boosters so always try to engage with a friendly team mate.
Zen’s Discord orb against a Pharah is very useful. It can be hard to hit a Pharah but Discording her allows her to be tracked more easily by you and your team and to deal more damage to her. If the enemy is running a Pharmercy the extra damage will really help. You are a target for a Pharah so knowing where she is at all times is very important. Being able to track a Pharah and hit her with at least one or two orbs can really help your team take her down.
Zen’s high dps and lack of damage falloff means he can contribute to breaking barriers. Charge your orbs as you round a corner and fire them into a Rein, Sigma or Orisa barrier to open the fight.
A significant part of Zen’s health is shield health that regenerates if you’re not taking damage. Ducking back around corner and then waiting for the shields to regenerate and then coming back with a full charged volley is a very good tactic.
If the enemy is far away enough, I believe you can Discord them so the later shots of a burst volley will deal more damage.
You deal more damage overall if you stick to firing orbs singularly however the charged volley can be used to in situtations where you think you might miss. Since it fires several orbs at once you can semi-spray it in across a region so at least 1 or 2 orbs hit your target. This can be helpful for hitting targets like Pharah or a fast moving Tracer.
When dive enemies like Reaper or Tracer are trying to dive you and use their escape skills, start thinking about charging your volley and moving to a safer or more advantageous location. Greedy Tracers or Reapers will try and return to attack you. A fresh volley in their face will punish them for this. At worst you will waste some ammunition. Consider waiting a second to start charging after you see them use their ability since you can’t hold your charge indefinitely.
If the enemy team has 3 or more dive characters and are focused on killing you or your other Support, it’s probably best to swap to Brigitte who can hard counter them.