I agree with this.
Financial pressures have also shifted the demographics on who has children (and their support network)
Concientious parents are having children later and fewer children. There's less experience gained through having multiple children. Smaller networks as there are fewer cousins (and less likely to be local), friends have fewer children. Support is more formalised and professional. NCT groups, activities, childcare. State support has declined (HVs, Sure Start). Access to these was decimated during 2020/21. While that is now a small portion of school starter's lives, the legacy is the connections that were never made, and the strain on services when additional support/ early intervention is needed.
Feckless families have always existed, and the proportion of them in some areas will increase as concientious people are priced out of parenting. The rise in aggressive (drug fuelled sometimes) behaviour deters people from calling out poor and anti-social behaviour because of the not-insignificant risk of initiating a tirade of abuse.
There have long been people distrustful of authority and education (and not necessarily without underlying issue/ traumatic trigger) and it's very difficult to target support or advice to people who don't want to engage. The stakes are higher in society now literacy is essential in the majority of employment and the role of academic qualifications has increased. Where parents lack life skills and literacy, that significantly restricts their ability and opportunity to do better for their own children. We have cycles of multi-generational families that have struggled since de-industrialisation changed their social frameworks. While many communities adapted and diversified, many didn't and fell behind.
I'm glad I had my children in the early 2010s before I had a smart phone (I went down the Blackberry route in that era). DS1 was very fortunately diagnosed with his SENs shortly before Covid restrictions. The paper trail went back to me flagging speech development concerns and raising them during a HV check with DS2 during the toddler years; a year later he was sufficiently behind for intervention which was largely done at nursery, and that got him "school ready" in time. I did all the "right" things... took him to parks, shopping, groups, and it was all stimulus for chatter. Chatting at home was harder, less varied.
For the DS1s born 10 years later, they were deprived of so much support, stimulus and intervention that got DS1 to where he needed to be. The gap is wider than it would have been in previous cohorts.
Trends were happening anyway but what Covid did was blow it into a sudden generational problem.
While we will soon pass beyond Covid-babies, the legacy is that support is not where it was in 2019 (and certainly not where it was 10 years earlier) and it is still harder to access support to be school ready. It will have also affected the experience of parents having younger siblings now as an indirect consequence.
There are also children with clear SENs being sent to fail at or be damaged by mainstream schools. That's a lose:lose all round as they don't get the support they need for optimum development and also compromises other children in need of a bit more nurture as well as everyone else, both in terms of resource avaliability and recognising the range of difficulty when it's been distorted by children beyond the range reasonably expected to be in that setting.
It's not a neat one issue problem. There's lots of layers of factors, some long term trends in society/ lifestyle, some political consequences and some ongoing consequences from Covid restrictions.