I think saying CM is set as a minimum and doesn't cover children's costs is disingenuous.
CM is a percentage of salary, if the NRP has a low salary CM is correspondingly low - not because the child costs less than other children but because that child's family circumstances are such that there is less for them full stop.
CM takes no account of divorce settlements and who received what and who has to fund what, divorce isn't necessarily even a consideration - in the case of ONS, casual relations and also non-married parents.
Some RP's get a significant amount out of divorce and don't have housing costs, get spousal maintenance and significant child maintenance. If this happens then yes, it is usually because the NRP has significant assets and or income and the children should continue to benefit from that.
I don't think that an NRP should contribute to RP & children's family holidays, above the maintenance contributions. Other than perhaps specific contributions to spending money made directly to the children if they chose to do so.
I say that both as -
An RP, receiving standard CM based on my exH's income and little else. He has occasionally brought uniform if it's fallen in his time, and paid the odd club subs. But not half of school trips (which I do think should be shared) and certainly not half of uniform, shoes, coats etc - which I see as the RP's responsibility; and
- as the wife of a NRP who pays the mortgage on his exW's house with no financial interest in the property, spousal maintenance and significant agreed maintenance in excess of CM which runs until the children leave tertiary education, plus pays an allowance to and various expenses for (phone, netflix, buys clothes, school books, school bus pass etc) his secondary aged child and covers expenses via a monthly allowance for his university aged child. And yes he has contributed to exW & children's joint travel as well.