Re: "Tin Foil" (why don't you post under your own actual name if you even are the same person?!)
lol, why would i used "variable running economy" as a branding term?! If I wanted to do that I'd use my tagline "Any Surface Any Distance" instead ! C'mon think a little here. Running Economy is an exercise science term. Yes, you got it right though...it literally means having good Running Economy over conditions that change....be it running up/down hills on technical trails in mud/rocks or even on a flat road track. I don't know how to explain it in more simple terms (except maybe to say the word "Efficiency"). But there are a lot of Variables.
To the next poster "Alavisca": Well UTMB is more competitive in general these days. So back to Kilian...who has already won UTMB: Do you not think Kilian can at least run close to 2:20 now in the marathon?
Say Kilian trains for a road marathon and runs 2:18. Then wins UTMB. Now you've got sub 2:20 guys winning UTMB. But then again a 2:12 marathon guy might enter and win (or lose to Francois who is most likely more of a 2:25ish type of guy). We could even say that perhaps it is a liability to be a super fast marathon guy and enter a race like UTMB as often the guys with marathon PRs over 2:20 have been "pure mountain guys" that focus on 100-milers in the mountains (probably more the trend with Euro runners and certainly not top US ultra runners). But perhaps it would be because guys who run sub 2:15 marathons (Max King etc) have traditionally focused most of their live on sub-ultra events and the track/roads and have optimized their shorter distance PRs to more of their true potential. It also be you generally excel and are focused on events that genetically suit your strengths (or speeds) more...but then we get into a whole "Nature Vs Nurture" debate!
As far as the Running Economy goes. Yes, in general if one has a really high Vo2max then they have more "wiggle room" because they don't have to be super efficient with their speed. Running Economy takes into account form mechanics as well as heart and lung adaptations and blood/energy flow. Velocity at Lactate Threshold matters, as well as other fuel utilization (glycogen to fat ratios for example). A 28-min 10km guy with a Vo2max of 80 (even with worse Running Economy than a 30:00 min 10km guy whose Vo2max is 72) in theory can run a 2:18 marathon much easier. But that is just measuring Running Economy on a flat marathon course and at 2:18 marathon pace. At 10km pace their Economy numbers would probably change quite a bit. So that is one variable..with the running velocity.
Another variable is the terrain. We're picking at "n=1" samples here when you are trying to cite just me (2:16:52 marathon PR by the way on an uncertified IAAF course..but I did run 2:18 at the Trials in '12) or just Kilian's one best downhill at Sierre-Zinal or Pikes Peak. As I mentioned earlier "n=1" stories are horrible data points and not good evidence to show general trends. Like I said: "sample sample size"...which is a common thing in MUT running because it's a pretty small niche part of distance running...
With past UTMB winners: Many have not run competitive road marathons or focused on that exclusively probably. So yeah, their PRs might technically be over 2:25, but that doesn't mean a lot can run closer to 2:20 or even faster. My HOKA teammate Tim Tollefson has been 3rd their twice and his PR is 2:18. David Laney was 3rd there a number of years ago and I believe he's run under 14 for 5km and maybe 2:17?
With longer races (above 1-2 hours), Vo2max isn't going to matter as much anyway. Running Economy is mainly the name of the game. Of course that can suffer with sheer muscle fatigue (cramps/dehydration/running out of glycogen etc) that will destroy their Economy. So that is another variable.
and FYI Sierre-Zinal is a net uphill race. The only really big downhill (steep) happens in the last 2-3km. It is a little technical there but mainly steep with some roots/rocks and slippery dirt. While, it generally trends downhill the last 10-miles it is a pretty smooth (non-technical trail). Much like the Pikes Peak downhill after Barr Camp. It's like a dirt road at times and the % grade downhill is only like 5-10% in a lot of spots. So yes Kilian probably isn't the best at those types of downhills since they really aren't that steep and technical. Just like he is obviously not the best at a flat 10km road race...but 29:59 (especially going out in 14:35 for the first half) is pretty darn good and shows enough "Variable Running Economy" (or we can use say "Range")...some of which he undoubtably trained for and almost got hurt doing running on his treadmill and doing 400m repeats and other "speed" this year. (or we can just say "Range").
But yeah, I think it is a little fishy that he says he did a "Sub 30-min VKand then ran a sub 30-min 10km in the same workout" in practice (or that he did 2 x 10km in around 30:00-min and sub 30-min in the same workout) but those workouts aren't actually posted on Strava? If I did a monster workout (that was better than my race performance in an actual road race) I'd be proud to post about it on Strava..with actual GPS data and HR data!