I mean dps ceilings are probably why you see such a rank variance in her as well.
Unlike mercy who needs to tap one button and spin in 360 degrees to use her unlimited healing, mercy can scales with better dps to hit +30% one shots and also top them off with 0 aim required healing.
Mercy does not cease to be able to heal even if the dps become 4x better at headshot accuracy because she also scales and may enable fight ending sojourn and others oneshots.
Meanwhile a moira has one static dps outlet that’s relatively harder to completely miss. There’s still tracking that seems 2x wider than a similar sym beam.
But that should mostly only apply to double jumping head crossing genjis and maybe the odd pharah.
So much of her resource bar is tied to her siphons that a 10% accuracy bronze dps who fails to do 30 effective dps dies to her, the immortal bronze rank 1v4 50 dps raid boss.
While a competent dps might just crit 3 bullets into her skull and gib her with a rocket before she might humanly react and realize she was gibbed in 0.2 a second.
While mercy and moiras numbers are both flat, moira is put into a rather odd feast or famine situation.
She can have more healing and damage on practice or paper, but she suffers from major diminishing returns the more competent the dps become at countering a flat 50 dps hero.
And as mentioned with proper aim, tracking, and ± headshots and above 10-50% accuracy, some heros can jump up from 30 dps bronze blunders to 100-300 dps shredders with much more respectable kill potential.
This is why it makes sense imo that you might see diminishing returns at higher ranks.
More competent dps makes over extending riskier and might deprive her healing bar faster while the team in turn also takes faster dmg. But if she can’t replenish it, shes a sitting duck with awful natural regen. And im not sure how to fix that tbh.