What's the point of a diagnosis, if there's no clinically significant impairment or distress?
The only reason for anything to exist as a diagnosis is to help understand something and alleviate the problems that arise from it. White people aren't diagnosed as melanin deficient, because white skin is not a health problem (albinism, however, can be -- in which case it would be helpful to diagnose). If someone's development was delayed, but they caught up, there's nothing to diagnose, anymore than if they had a period of malnutrition that stunted their growth for a bit but recovered by the time they reached adulthood.
And "broad autism phenotype" doesn't make any sense unless you have a good idea of what "autism" is. A collection of disparate traits doesn't cut it.