I agree with you op that people are doing the best they can with the tools they've got.
My mum had a terrible childhood and was ill equipped to parent well. She was however a very loving person. But she made a lot of mistakes.
Her mistakes were very damaging to me. But she really was trying her best.
Because she was really trying and never meant any harm, I don't blame her for what happened.
She emerged from her own upbringing scarred and did manage not to pass on all her problems.
She achieved a reduction in generational trauma because she really gave it everything she had in terms of love and a willingness to learn and do better. In fact 4 decades on, she is much better equipped with language and understanding and reactions she lacked before - and if she had her time over would do a better job because she has done the work in going within and being open to change and (constructive) criticism to improve herself so that she can truly express the lovely heart she always had but which was impaired by her own abuse.
None of that alters the fact that I was badly scarred... But I also am grateful for the gifts she gave and the example she set of loving deeply and seeking personal growth.
So I have also self examined and sought to heal, and my own children's childhood is a thousand light years away from what she suffered because she was brave and faced how she was and improved herself inch by inch.
Her relentless search for better (and mine) means that her own grandchildren can enjoy healthy relationships. Like you I have used my experience to equip my kids with some epic emotional understanding and relationship skills.
That's where I'm coming from, so I know that the hand we are dealt does not have to define us forever and we can end our lives in a very different place to where we started it. But scars are deep and it isn't an easy path.
Some people don't even try though and stick to their unhealthy ways. For those people there is no improvement and those around them will always suffer.
A parent relationship is not a romantic one. I think if a damaged person is too damaged to be a partner without causing serious harm to their loved one, then they should ideally seek to heal before they couple up.
In reality, everyone wants a companion and often that doesn't happen and people get involved regardless of the damage they cause. Often they don't even realise it, and that's understandable in many ways.
It is incredibly unfair that a child upon whom emotional wounds are inflicted should have their natural basic desire for a life companion affected by their inability to be in that relationship in a healthy way.
This is why adverse childhood experiences are so hideous because the effects are so long lasting and are passed on unintentionally.
I think if any romantic partner did not want to be in a relationship with someone because their behaviour was too damaging then that's a reasonable decision.
I think sympathy for everyone involved is fair.
If you are the damaged person, I think it is possible to improve your reflexive reactions if you find ways to do the work.
Wish you all the best op. It takes courage to even look this stuff in the eye.