Yep I know what you are saying as I have done both marked and unmarked courses, however I have always found unmarked courses preferable to marked not least of all because I know where I am at any given point and that I am not following markers that may have been tampered with and I do like the fact that an unmarked course can even out the field, in as much as a marginally slower runner that can navigate better than faster one may just be able to take a better line and put themself on a par with the faster one thus giving the faster runner the satisfaction of having to push themselves harder which in turn makes for a keener race.
Every Event I have ever done (and I have done several )has always been done on sight, as I find that the hours spent poring over maps and then putting my understanding of the route into practice on the day makes for a complete experience for me at least.
As to unmarked v marked making for a pure race, that has not been my experience as I have in the past beaten folk on marked courses that have beaten me in the past on both marked and unmarked courses and of course vice versa.
Of course as you will appreciate in an ultra race it is not just about a physical race, there is also a very big mental race that has to be played out by each competitor in order to get through the lows, not to mention the the ability to overcome sleep deprivation if the event is long enough to take you into a second day,
TBH it is all pretty much what floats your boat a and I am glad that UTS went well and was enjoyed by you and others.