To be fair, I agree with that sentiment about the need for the race to be of a particular minimum length, although I'm not really sure why. It's likely partly to do with the idea that the World Championships are a higher status than your average everyday ITT as part of a stage race, and every other standalone ITT outside of championships (so obviously also the Olympics, the Continental championships and for some people the Commonwealth Games, Pan-Americans or similar) doesn't tend to draw the same level of field as the Worlds so it should be made a greater challenge. That's kind of received wisdom, but then you have some people who are great TTers who specialise over a middle-distance kind of route, like Adriano Malori used to, who would never stand a chance on a Worlds course because he would fade as distance tended upwards, so there is a case that much as the Worlds RR varies in profile so all kinds of different riders get a chance to win, so the Worlds TT should as otherwise it's something of an annual get together of specialists, in which case why not just have the Chrono des Nations at the elite level like in years gone by, and measure performance across a consistent course? Havinig it vary more in course would also make it harder for the TT mayflies that have been a problem in the womens' péloton in recent years too, with a group of veterans riding few road races and staying away from the elite calendar, basing the whole year around that high profile TT, and then disappearing and never showing the rainbow stripes in a major race all season (notwithstanding that there aren't that many ITTs in the women's WT stage race calendar at present).Why?
The other factor in the received wisdom of the championships needing to be longer is probably to do with conflation with other types of races in the calendar where the length is a deciding factor for prestige; the most prestigious stage races are three weeks long, compared to one week or less for most of the rest of the major level stage races (sure, races like Portugal and Colombia are 11-15 days, but they don't have the same field). The most important one day races are the longest on the calendar, with the five monuments all being among the longest days' racing on the calendar. Milano-Sanremo pushes 300km, all the others bar Lombardia are in the 260km area, and Lombardia is 240-250km but with the climbs it has, takes the same kind of length of time. The World Championships RR is constantly up around 260km. Looking at last year's World Tour, the only other one-dayers that match up to that in distance are Amstel Gold and Gent-Wevelgem, which are among the most prestigious non-monument classics. The outlier is definitely Plouay, at 248km, as it is outside of the traditional 'classics season' and isn't a race which is considered as particularly specialised; for the most part other established single day classics on the WT calendar range from 180km to 220km and largely fall around the 200km area. A cursory glance through the Continental Tour one-dayers shows the majority falling in the 180km to 200km range, tending upward as race status increases, and Paris-Tours, perhaps the most prestigious and traditional non-WT classic, is the longest at just under 220km.
Plus, of course, cycling is first and foremost an endurance sport. However, while distance is a major factor in difficulty in road races, especially one day races, because of the pack nature of the sport, so wearing out and dropping the helpers is a crucial element of creating intrigue and inferring prestige, I guess that doesn't automatically mean that distance would have the same impact in a contre-le-montre as it does in road stages, where we've frequently seen distance be a factor in who contends races, such as Chloé Dygert hitting the wall completely at the 130km mark in the Worlds last year after looking like the strongest rider out there before that, and the way that Óscar Freire seldom won anything at the 150km mark, but came into his own the longer a race was, with his most prestigious victories coming in the longest and most arduous races of all, winning three world titles and three San Remos.