I think there are so many situations where the system is absolute rubbish.
Just anecdotally, from my own experience:
My DD's father left when she was a year old. I earn more than him, but still struggle to pay for her to be in full time childcare on my one salary - while also paying my mortgage and bills...etc.
DD's father lives with his girlfriend and her 3 children.
He has to pay so little maintenance it is ridiculous. He technically has her for 3 nights a week, but it is literally that - I pick her up from nursery and give her dinner, he takes her home and puts her to bed and I pick her up at 7am, give her breakfast and take her to nursery. His costs of being a father are £50 a month. It is pitiful and I don't think it's fair.
Then my Boyfriend has shared custody of his DS. He has him with him from Wednesday to Saturday every week.
He pays for nearly all expenses - his phone, uniform, clothes, school trips...absolutely everything.
Yet he gives his DS's mum £250 a month thanks to CMS - and we don't really know why! She is officially the 'resident parent' because she has him one extra night a week. She earns more than DP and lives with a wealthy Partner. She has no childcare costs (when he was in childcare they paid for the days they needed - so she paid for Mondays and Tuesdays and my DP paid for Wednesday-Friday). It feels mad to me that my DP is paying £250 that his ex doesn't really need and I'm getting £50 a month that is way less than my DD needs.
It is baffling.