I can understand your disappointment/expectations.
We are all different. Your child is likely to be amazing at plenty of other things, he just might not be academic. Not everyone is suited to the way schools teach.
IMO, intelligence isn't necessarily genetic, another huge part of it is dependent on the child's experiences.
In the nicest possible way, if there are no learning issues or ND, has he had lots of different experiences? So, not every child would be good at sport, but those that regularly go to the park, soft play, swimming lessons or even do a relaxed sports club for fun, generally have better coordination and gross motor skills than those that don't.
Do you read a bedtime story every night, does he do some art and craft? Do you go out to different places such as museums, theatres, parks, woods, seaside.
I am not judging your parenting, just trying to explain that the more the do/exposed to, the more they learn. Just a fact that reading, being active and creative is great for brain development and concentration. However, it doesn't mean he'll be academic.