I am not dismissing it, because it does tell you something, which as I said is the range of experiences. You are right it is a blunt instrument but you say you are aware of the limitations of straw polls - the major limitation is that they are not especially accurate and should not be over-interpreted.
I do agree that if you take just this thread into consideration it seems as though more than 5% is likely, but as somebody else said, more than 5% what? You keep mixing up numbers - more than 5% autistic would be surprising, more than 5% ADHD + Autism not especially, and more than 5% SEND is not surprising at all because SEND is "officially" at 20% anyway and has been going back in reports right to the 1970s.
I don't need any validation of anything personally, but I do think that, collectively, we need to be careful around the subject of the validity of these diagnoses, because despite scientific consensus, it appears to be an alarmingly widely held view that they are some kind of conspiracy, or massively inflated because they are somehow desirable e.g. as an "excuse", and this is damaging when such views are held by people who have real influence over policy - members of local government who are responsible for funding decisions, teaching staff or management in schools, or even higher up in the government, as seen in the US.
I am very happy to talk numbers, because I also find it interesting, but I am not especially interested in rehashing all the old chestnuts like ah it's the environment - they just need to be let out to play a bit more etc. I mean sure, that would be great probably for all children, I would fully support more outdoor play in schools, but lack of playtime doesn't make a non-ADHD child into a child with ADHD. Or this idea that because we are now catching many more children and hopefully gaining a more accurate picture of prevalence that this is some kind of runaway train which needs to be stopped before 50% of the population have it - that's not an accurate picture at all and that becomes obvious as soon as you look at the actual context for these "skyrocketing" rates the papers like to talk about. Or look at properly researched studies/surveys, rather than going on vibes.
I would be really, really happy to have a discussion about numbers where the myths which are stupidly easy (but time consuming) to disprove don't even come into play at all, but weirdly enough when you get people who have gone past those myths and understand how it actually works they also don't seem especially worried by numbers.