Sorry, this turned into a giant post!
Ninx and someoneoutthere, doubting the DX is very common, and nothing to to with the initial denial phase. I was struck with your description of your DS being hypo-sensitive after 'More than Words', someone, as my DS is mostly hypo and he really didn't seem to be stereotypically autistic. He has never had much difficulty with routine, perfectly happy with transitions (so long as they go his way.) But he was very late talking, flaps and jumps so I wasn't left in much doubt! He is quite bright with a 'spiky' profile, some of his early spatial reasoning tests were on the 98th %ile, but he has deficits in the theory of mind areas which affect his ability to answer why and how questions.
There is a resource called 'Language for Thinking' which is very good, and can be used at many ability levels. It's a book of about 50 small scenarios (with a picture) with different levels of questions to develop a DC's inferential thinking, ie reading between the lines, suitable from about 5 or 6 til about 10 or 11. My DS used it at school and I use it with the DC I support. (I'm a TA)
With good interventions and just time sometimes, DC with ASD can make excellent progress and they will develop and reach milestones, just maybe in a different order to NT children. My DS had big issues with eye contact, but he seems to have grown out of that. As time has gone on and work at school has got more abstract, his deficits have become more apparent. I'd say he was obviously autistic at 2 - 6, less so at 7 - 9, but now he is 11 his peers have taken off socially and intellectually and he is lagging behind again. His Maths is great, but although his literacy is mechanically correct, punctuation and spelling good, the content is immature. Literacy was good when these points were the targets.
There is a view that it may be better to talk about autism in the plural, autisms, as the spectrum is so broad that each person presents so differently that it's hard to give it a single DX, and that it seems to be co-morbid with so many other things, autism with SLD, or with dyspraxia or with dyslexia or hyperlexia or epilepsy or ADD or ADHD or APD, etc etc. Amberlight has some really interesting theories.
The important thing is that you get some good, appropriate support at school, so your DC can reach their potential, I suppose. I find the whole subject so interesting that I tend to go off on one sometimes, sorry! 