For a start, my kids all receive the same experience from their Dad. If we divorced, he'd have the 3 kdis the same amount generally speaking. My friend has 2x2, one involved, one not. I can't imagine how hard it is for the older lad never seeing his Dad. He sees the younger ones Dad a bit, but not as much as his brother. That's a lot of inequality.
Now make the one of the four hypothetical Dad's rich, he does 50/50 care and the kid always gets new stuff, no other kids. Loving step Mom. Richard grandparents willing to pay for education and will leave a decent inheritance.
Dad two does Eow and a half decent job in between. A new baby sibling and an indifferent step Mom who moans he comes over too much. Grandparents around a bit, but not much money.
Third has a chaotic life. There one month, not the next. Three other half siblings to three other women so he barely has a relationship with other kids as access is chaotic. Always a new women. grandparents are pretty absent and toxic when they're around, always blaming the women.
4 disappeared before the baby was born. Never been around. No grandparents. Nothing. Just a gap.
You don't think the impact on those kids when she's contemplating the next baby is different to full siblings?