I think with your view of the Diamonds, you are correct. But out of the three, I feel like Yellow is the one most redeemable.
I know almost everyone sees Blue as the ‘most redeemable’ of them, but she’s blatantly worse than Yellow. People really got tricked by the crybaby trick, but she’s the more violent and murderous of the three.
She is explicitly described as a “Shatterer” by Garnet, and immediately jumps to killing Ruby when she and Sapphire accidentally fuse. In comparison to Yellow with Peridot, who gave multiple chances (and didn’t even consider shattering her for her insubordination) she is a lot more cool headed.
Blue is very emotional, while Yellow is very pragmatic.
As Blue during Era 2 is doing nothing but wallow in her grief, and White (literally) stuck in her own head, Yellow was carrying the entire Gempire on her back, so no wonder she’s a workaholic.
And also, in their pseudo-redemption in SU:F, Blue basically gives people happy drugs (very helpful, Blue) and White uh.. lets people control her body (Very helpful too, White). While Yellow is literally bringing people back from the dead, dismantling her armies and also taking apart the Cluster piece by piece. She imo, seems to be taking redemption much more seriously than Blue and White.
Of course, she’s still a horrible person. They all are, but I think Yellow is much less of a horrible person than the others, since she’s actively trying to fix things, and is just a more pleasant person to be around.
While Blue shattered gems for their crimes, Yellow force fused broken victims of the war into monsters, one large enough to destroy the very Earth they sought to protect.
When Pink died, Blue retreated into herself and went against her typical principals by keeping the Rose Quartz gems in tact. Through her grief, she became docile, but Yellow became hostile.
They sort of swapped moral compasses.
Blue Diamond was probably more cruel than Yellow prior to Pink's shattering, but outside of Garnet's retelling, we don't see this on screen, which is probably why people give Yellow more flak.
What we do see on screen, is Blue Diamond's penchant for projecting her grief and sorrow onto the other gems, rendering them immobile. She often used this as a weapon against Pink when Pink misbehaved or embarrassed them.
Blue Diamond projecting her happy, content emotions when she's finally at peace is more so used as a spa for gems to refresh themselves. Blue Diamond likely hadn't shattered gems in a long while- wanting to instead preserve things, especially if they reminded her of Pink. So while Yellow Diamond's work seems more hands on with reversing the cruelty of their tyranny, Blue Diamond's work is still symbolic of what she had done to other gems within the past 6000 years. She's not the one who built that cluster after all.
White Diamond letting other people take over her body is supposed to be symbolic, as she's allowing herself to turn off color to experience what its like to be in the shoes of others, but its ignoring the fundamental issues of White's morality and what she's done here.
White pushed for perfection, she's the entire reason gems are rejuvenated and shattered due to their off colors. She's the entire reason they've taken over planets and mass murdered the organic life there. She judges your personality and erases it, possessing your body for her whims.
White remembers her experiences when other gems take control of her, but that's not the case reversed. Pink Pearl didn't remember anything within the 6000 years she was controlled. She allows other gems to take over her body to feel powerful- to take control of someone else. Morally speaking, I still find this to be inappropriate. White Diamond takes great pride in what she's doing here, but she's still ignoring the organic life forms she's affected. She still believes the Earth to be disgusting- that Steven is better than the Earth- that he belongs with them on Homeworld.
I think in order to redeem White's character- she has to experience what Pink experienced. She needs to find the beauty in ALL life, no matter how small or strange. She needs to find the beauty in imperfections. Better yet, find even the ugly in imperfections and still learn to accept it.
If she were travelling planet to planet to undo the damage she caused- or even fixed their homeworld planet, (Which they unfortunately canonized with the movie, they CAN reverse the damage they did to planets biologically.) I think that would be more fitting for her character. She hasn't been directly involved in the livelihood of other gems in so long- Blue Diamond and Yellow Diamond were hands on with that. White simply watched from afar and made sure Blue and Yellow carried out her will on her behalf.
It's good to show her respecting lower gems, but I think she needs to go further and find respect for non-gems, which she has yet to do on screen. That's why her redemption fell flat to me.