Henman is the man because slam performances trump everything and 6 slam semis are 50% more than his greatest rival for the accolade (Davy).
Before Murray won the USO, very few people argued that he had accomplished more than Delpo, because the big man had achieved more at grand slams than Murray had i.e. all those slam finals, masters series wins and other titles were trumped by Delpo's solitary better performance in the slams.
It follows therefore that Henman's better slam results trump anything that other players might have done away from the slams.
If Davy had matched Tim's slam record then his other achivements would swing things his way - but the fact is he made 50% fewer slam semis than Tim, QED Davy is not the best player never to make a slam final.
There are 10 types of people in this world. Those who understand binary - and those who don't.