Just to give another perspective, much of your description fit my son aged 5. Very bright (not quite as bright as yours but early reader, very eloquent for his age, Lego whizz, very good reasoning etc) and VERY difficult indeed. Very affectionate but also incredibly strong-willed with an explosive temper. I relate to the medicine issue so much!! We gave up on any medicine that wasn't essential because it was a case of force-feeding him it. No amount of cajoling, bribery, argument, threats would work and he went absolutely berserk over it.
He was very strong-willed, would frequently say no for the sake of opposing us (it felt like) - ruined many a day out with sulking, kicking his siblings, calling us names under his breath
We had to communicate very carefully, explain things, pre warn him about trips or even going to the shops for gods sake, and even then about 50-% of the time he would kick off about something. We applied consequences and that worked to some extent, but sometimes it would just enrage him and he'd smash up his room, throw things ...
And at school, nothing. Reports said he was easily distracted and sometimes had trouble obeying classroom rules, but otherwise fine. At least during school term we had relatively fewer outbursts. The holidays were SO hard.
Anyway ... fast forward and he is now 7, will be 8 in April. We endured all of ages 5 and 6 hoping he'd grow out of it, but by 7 and after a horrific few weeks last summer holidays I took him to the paediatrician who referred him to a child psychologist. He's had about 6 months of talking therapy now and honestly, between this and his increasing maturity, we are finally seeing the light at the end of the tunnel. He still has outbursts of rudeness, impulsiveness, hyper etc but he is much more in control, and if he does explode we can generally help him calm down. He has his 'calm' activities like reading in his room. We can negotiate, we can explain, we can compromise. He understands our point of view even if we sometimes have to agree to disagree on things.
Interestingly the psychologist is reluctant to diagnose ADHD; she says many children struggle with developing executive function and he may just be late in this aspect of his development. Which, combined with intelligence and a strong will, is a recipe for the type of explosive behaviours we saw. (I agree with previous recommendation of The Explosive Child as a good read.)
The only thing that helped was patience, explanation, strict application of 1st warning and then (fair) consequence, talking, hugs, more talking - and the therapy too. Old-fashioned discipline was a disaster.
I don't know if this is helpful but maybe be open to the possibility he may outgrow it. Eventually!