Lotta, I recognise your caseload issues well, but I suppose I challenge the idea engagement issues are primarily about a lack of thought. I think they're more usually reflective of disenfranchisement, disadvantage and extreme stress.
I work with a colleague whose main role is in something called Multisystemic Therapy, which has many applications, but in our area is targeted at the hardest to reach families of teens who are persistent reoffenders. It's a behavioural therapy and she has to work very intensively with families, with a member of the team on a 24-7 on-call basis and they work across home, school and social settings. As such she does a lot of work in families who have long histories of non-engagement. She says in practice, the difference in everyday interactions in family homes in terms of how people interact is much less than we imagine but that there's far more stress, often related to poverty, with unpredictable outbursts and responsiveness and consistency can be lower, in part because of sort of persistent low level mental health issues or more accurately, poor levels of mental well-being. For this reason, outcomes in MST fall solely on the team providing therapy. No one is allowed to say 'well they just don't want to engage'. The team HAS to find a way to make them engage, and their outcomes, as a result, are second to none (though you'll recognise resourcing is the white rabbit here).
I do feel they are onto something in terms of the causes and foundations of engagement. I have seen first hand the impact of reduced mental health when I had PND, which was like a bolt from the blue. Looking back, it's almost hard to fathom the extent to which my thinking was not 'me', or how living with stress impacted on my own thouhhts, feelings and behaviours as a parent. However, I had SO much privilege in terms of my background, education and in how I went about securing services for myself that it was a mere glimpse into what families face. I did a PND group with women that once I would have been advising on how to interact with THEIR babies. I sat with an Occup Therapist who talked to me about how to interact with mine. It was simultaneously both the most soul-destroying and eye opening experience of my whole life and it radically altered my perception of the barriers to engagement I had long perceived differently.
I am no longer even slightly surprised that parents fail to engage with many services, not least adult-child interaction therapies. It feels like someone is judging your very soul, it's almost wirelessly awful and I say this as someone without any of the barriers faced by many hard-to-reach families. I understood the process. I could read. I had a faith in the culture of therapy. The people offering it to me were 'people like me' in terms or class, culture and background.
While I do feel you are right in your comment about how 'overthinking' can be used in debate to silence and I understand your point better now having looked back at the conversation, I think that as a profession sometimes we have a poor understanding of the broader interaction of thoughts, feelings, experiences and behaviours and of the mechanisms of changing human behaviour, despite having valuable skills and knowledge to impart.
I was amazed to learn in my own CBT treatment, for example, of the ways in which rumination (or overthinking) and reassurance seeking can exacerbate and maintain anxiety, while avoidance of appointments with professionals was recognised as a potential symptom of clinical anxiety. I had never heard of this in my career, even though paradoxically I'd done a lot of training and in service on anxiety and CBT in my autism role.
I think that endless ruminative research and discussion on decisions about, say, childcare can be unproductive, and that most parents need to be supported to listen to and trust their instincts on what works best for their families. This should not imply that there shouldn't be due thought and research put into that where possible, but look at the suffering and ire caused by endless poring over 'research' based parenting.
Bottom line, OP? You don't feel comfortable with this setting for your son at this time. The verb ending stuff is just a red herring. You don't feel comfortable and you don't need, in this instance, a lot of research to make a decision for you, because your reasoning is somewhat emotional, and emotions can't be solved with recourse to scientific literature. My advice to you as a parent (not a professional) would be to throw all reason aside, then set aside a chunk of quiet time when your child is in bed to just sit, breathe and notice your thoughts and feelings about this issue as they arise. Instead of getting tangled up in any one line of thought, imagine each thought can only be one sentence long, 'listen' to it and let it go, perhaps labelling feelings or atmospheres that arise with one word or a short phrase - worry, judgement, concern, uncertainty, discomfort, unease, not in line with your views/values etc. I'd do this with an open mind, you might notice some new information about what you think in approaching the issue in this way. I read once that 'the stance to take is one of open awareness, like a butterfly a lighting on a leaf, rather than examining your thoughts with a laser sharp focus'. It's a great technique for decision-making and often very illuminating. I think you already know whAt you want to do here.