I must admit I was staggered when the scale of the earthworks proposed to build the runway was revealed (when was that - about 10 years ago now?). I thought the Shelco proposal was novel and probably workable. I was taught on the first day of my engineering course "an engineer does for 19s 6d what anyone can do for 21s" (you can tell it was quite a number of years ago!). Shelco applied that principle whereas what has been built uses the "money no object" principle typical of many public projects.
By the way, I understood that the Americans have vetoed the idea of the Ascension runway being designated as a weather alternative, only allowing the once a month scheduled flight to provide transport home for Saints working on Ascension and the Falklands. (Ascension would be usable in an emergency, of course.) So the nearest diversion you'd probably want to use is Walvis Bay or maybe Windhoek. All complicates the fuel/cargo/pax load calculations versus commercial viability and possible subsidy required.