Damo, I agree that 1-2mm scars are most common and the radial pattern you refer to can be more pronounced than that so I agree that the trych closure has its limitations. A scar is a scar and as you mentioned darker pigmented patients can indeed be more prone to wider or raised scars.
Obviously the other option is to have hair implanted into and around the linear scar (once everything heals) because IMO there is more control of angulation and selection of donor hair so the grade and distribution is more natural in appearance once it grows out. IMO most surgeons would then utilize a double-closure technique in place of a trych closure.