I've decided to reveal my secrets. This is my Ying strategy laid out as best as I am able to write.
There is more than one way to use resonance. While it may seem like resonance is a boost for your shatter ability, it can also be used as a passive. Resonance allows your illusions to ALWAYS explode, even without ever using shatter.
Shatter causes your illusions to stop healing, and should be used sparingly. The exception is if you have misplaced your illusions, or their position has become obsolete for team heals. When this happens, flushing your illusions out with a shatter is often their best use.
This means that initial placement of your illusions is important, for them to have offensive effectiveness. Doorways make excellent locations, covering two sides with heals and providing an explosive barrier. Next to corners is also good.
Since illusions heal by auto aim and explode in an area, placement can be generalized. The trick is to use distance to help adjust your placements. This frees you up to engage in combat with your weapon, to a degree. By spamming illusions into the enemies' line of fire, you can gain the damage of shatter and the healing of illusions simultaneously.
Dimensional Link should be reserved as an emergency escape, and is easily your best tool for addressing flanks.
Compared to Life Exchange, this build is only slightly less healing, by aggressively keeping illusions on the field. Compared to Focus Lens, you might do less damage. This build uses resonance to balance damage and heals, producing a greater output overall.
Level 5 Tangible - Useful for surviving Jenos ultimate and sniper shots. Every point counts, so this is an all or nothing card if you want to make personal adjustments.
Level 4 Spring Bloom - The single most crucial card for using Resonance as a passive ability. This allows you to place your illusions aggressively. If the enemy destroys an illusion, you get your cooldown to replace rapidly. You might want level 5, but if you plan to play with this style, I recommend at least 4.
Level 4 Ephemeral - I have problems with reloading too much. Very likely a place I could improve the build if I were a better player. Mesmerism is an excellent alternative, since you'll be spamming illusions constantly. This card is the most adjustable to playstyle. I recommend tweaking it as you try getting comfortable with the build.
Level 1 Carry On - Ying used to have more duration on her illusions. Changes have made this card necessary to a degree, but timing out your illusions allows them to explode. A minimal investment seems like the best choice. You can adjust carry on, making Chronos more, or less valuable. Chronos is an expensive upgrade. Level 1 Carry On pairs best with level 2 Chronos. Because, this card/upgrade pairing meets the minimum for keeping 2 illusions on the field.
Level 1 Rewind - This card is a must, but you only want one level. When used, you'll cause extra explosions, caused by going over your two illusion limit. You'll end up with illusions at low health. Easily destroyed, they explode and then Spring Bloom turns that into fresh illusions.
Chronos v Moral Boost First?
Not an easy choice. I prefer Chronos since it takes time before Ying can get both illusions out. This build can quickly generate ultimate charge in my experience. Chronos helps you do the combined damage and heals this build strives for, and that charges the ultimate.
With clear exceptions, upgrades are player preference, and you shouldn't let people judge your choice. Experimentation should be encouraged.
Increase your maximum Health by 250.
Reduce the Cooldown of Illusion by 2s when an Illusion dies to an enemy.
Increase your Reload Speed by 32%.
Increase the duration of your Illusions by 1s.
Spawn an Illusion with 20% Health when you swap to the spot of a dead Illusion.