I think like many who live in countries where benefits tend to come with conditions like-
-being contribution based
-being time limited
-being fixed (ie no increase if your outgoings like rent, no. of children increase)
I find the current British system, seemingly devoid of all 3 of the above conditions, a bit baffling. Almost like it was (accidentally, I presume) set up to trap people into a form of "never quite enough" dependency and keep them just desperate enough to accept unfavourable employment terms and some very inflated outgoings.
However you can't set up a system, allow people to make permanent life choices based on the existence of said system and then whip from under their feet.
Any changes would have to be phased in and other systems would need to be up, running and working (in practice as well as theory) before the goal posts got moved.
Maybe the amount of untaxed earned income needs to be raised.
Certainly there needs to be a far better system of making NRPs provide realistic levels of economic contribution for their children.
Might be worth casting an eye on systems other countries use that work well enough without causing undue hardship and social issues. However that needs to be done by looking at how individual policies function in the context of the whole system, not just cherry picking a superficially attractive bit and expecting it to work flawlessly outside of its original context.
On top of that there will also have to be a transition period allowed for a mental adjustment. One of the marked differences I see in people posting on here, and the people I live amoung, is how they assess their position in terms of extending their family. On here people often have a "how well things stand now", outlook, a quite optimistic "things probably won't get worse" sort of view. Whereas where I live the emphasis is on how you would cope if things went bent. Like a lost job, an accident, or an illness. Which tends to be a more pessimistic process (ie "It COULD happen to me and the safety net won't be enough if we have one more child") and more often than not it results in a smaller family. Which means a lowered population growth rate, carrying implications of its own.
Those difference IMO are neither genetic, nor innately cultural. They are environmental. They are connected to a reality of just how hole free a safety net appears to be in the context of a larger family. Expectations of support aren't created overnight, by the same token they can't be scaled back at the speed of light. It would be supremely unfair on the children in the mix if that reality wasn't taken into consideration.
Things could be done differently. However unless existing systems are replaced with robust new systems and a period of adjustment is allowed for, undue hardship is likely, and civil disobedience not an utter impossibility. Anything saved from an overly rapid, unprepared for "changing mindsets" and cost cutting exercise could end up costing far more (economically and socially) due to unintended consequences.
Certainly I think there is room to suggest that the current system in Britain is playing a role in an overheated house price/rental market and suppressed wages. Perhaps also the small, but not negliable, rise in second and even third families, which may be carrying a risk of poorer outcomes for the children involved. All that suggests that unintended consequences are not always de-bugged out of a new system before it gets rolled out to the British public.
I'd immagine in order to make change as painless as possible for the small people with no power and no say in the matter, you'd need a couple of decades at least to transistion from the current system to something different. With pleanty of up front warning, so expectations can adjust and the can isn't just kicked down the road.
Bear in mind also that if a need vacuum is created, it will get filled. People won't curl up and die of "not enough" to provide satisfaction for those that disapprove of them. They tend to fight back if an unfulfilled need they have now is pressing enough. Over here we do not have the costs of your benefits system. On the other hand we have plenty of black markets (employment/housing/everything else) and rule bending where necessary. Which I am not sure the British mentality could cope with as well as they cope with a potentially inflated, but essentially controlled and regulated, benefit system.
Which I guess is a very long way of saying "be careful of what you wish for, it might not look the way you think it would if it came true"