Getting a gold hero that you've already maxed from a dust chest pull is really punishing. Sure, you get 2x dust as a reward, but the most you can get is 30 dust (15 shards max pull x2). You've essentially made a net loss of 70 dust. This is really demoralising and needs a rethink. Could you not adjust the pool of available heroes to only include heroes that haven't been maxed?
#Remove maxed unique heroes from dust chests
indigo sail
lyric gorge
It is the same for a hero chest pull... maybe worse. Even at 2x dust for 50 shards it winds up converting to 5-15 shards of a (hopefully) different unique-level hero. If you're unlucky enough to double-up, you could potentially go from 50 unique shards to 10 yellow dust on the pull. If someone spends actual money on the pull, it's borderline criminal.
I'd imagine adjusting the code to narrow the pool might be prohibitively difficult, but to my thinking a relatively easy insert into the algorithm would be to adjust the try/catch (or IF or whatever is actually used) that triggers the dust conversion to test for unique-tier and either loop to a re-pull in the case of dust chests or try/catch the next hero in the table for hero/event chests.