As always, pb has excellent advice. I also agree with blackcat's pedi suggestion.
It also sounds like there might be some confusion about which behaviors are suggestive of high intelligence, and which of ASD. Many of the behaviors you describe could be perfectly normal--in a GT toddler.
So in the context of concerns, it would be reasonable to consider the motor skills, orderliness, language, toilet training, etc., to be "normal", because they are not delayed.
If you are looking for clarity about ASD/OCD, the target category of behaviors would be restricted/repetitive behaviors, or rigidity. For ASD, you would add social communication and interaction skills. TBH, your posts to date don't suggest deficits or delays in SCI, nor do the RRBs appear to fall substantially out of the range for toddlers. It's just that the range of his awareness is wider than that of many other 18-month-olds, which usually means that the gap between the world of which he is aware, and the world over which he has control, is even wider than that usually experienced by toddlers, which naturally would be expected to raise his anxiety--which contributes to his need for order and predictability. Having raised a number of toddlers, and worked with many, many others, I can say that it actually is common for 18-month-olds to pitch fits about not being able to finish little tasks they've set for themselves. HIs tasks are just a little more sophisticated than those of some other toddlers.
Of course, we know only the tiny slice you've shared about your son's development, so it may be that you actually are seeing RRB and SCI symptoms. If that is the case, I would suggest focusing your symptom reporting on those two categories, when you are listing your concerns for the pedi.
With respect to acknowledgment from your pedi that your child is above the norm, I would agree that, if this is an important part of your relationship with the pedi (and it may become more important if you will need this person's role as a resource for addressing GT needs in the future), then you should consider a new provider.
