This is so true and our experience.
We adopted a 3 year old "with no issues". No issues? Ha bloody ha!
Either he just about held it together at nursery/school and then had massive meltdowns on the way home or the second we got through the door. Or he was fine at home and caused havoc at school.
Anxiety, low self esteem, not unstanding social cues, unable to make or keep peer relationships. It was a complete smorgasbord of emotional turmoil.
We asked for additional adoption support a number of times, but in the end we decided to pay for private support and he had counselling sessions at regular intervals from around 7 to about 18. It cost us an arm and a leg. I am glad we did, and he still talks about her. It gave him an outlet to say stuff he didn't feel he could say to us. We knew specific times of the year would trigger emotional fallout, so I was able to pre-book a series of sessions beforehand, and start them before he needed them.
When I approached SS again when he was about 14, as he was becoming difficult and I knew there was weed and other drugs involved, they were worse than useless.
Basically I feel that the state offloaded a child with obvious issues (obvious to them at the time but denied) on to us, and by doing that saved themselves 15 years of Foster Care costs and other costs as he would probably have got more support being in foster care.
I love him very much and I am glad he came into our lives, I couldn't imagine parenting any other child, but bloody hell, it's been tough at times.
Edited to say I also thought he was neuro divergent, but that was denied at school. Everything was hung on the hook of "attachment issues". At 20 he was finally diagnosed with autism and also put on the waiting list for and ADHD assessment - that was three years ago, still waiting
So on the one hand, school used attachment issues as a means of evading ASD or ADHD support, but at the same time SS were saying he didn't qualify for adoption support. We felt like we were between a rock and a hard place a lot of the time.