Per usual, you provide a wealth of information and salient points.
What I will say is that there are several "hobbists and independents" making much more racing here, than many WT pros. Gravel in the US has already supplanted XCO and road (which was not a monumental task). I think the advent of income via social media has changed the game for gravel in a very good way.
I think the social media side of things definitely helps gravel, but it does have the impact that it's more seen as something to experience than something to watch in the way that you would a road race or a cyclocross race. But we shall see how things develop in that respect, since the discipline is in its infancy as a pro discipline (although it's worth mentioning that though I would agree it's quite likely some of those early Euro MTB specialists who started beating the Americans in the early 90s were to be discussed elsewhere in the forum, it's also true that testing has been lax or minimal at many gravel events and I think that's part of why the UCI has tailored their events the way they have as mentioned earlier.
The other aspect of what I suspect the UCI may be doing with gravel is more to do with - hear me out here - sportscar racing.
You see, most people would agree that the most prestigious motorsport format is Formula 1. I personally have many problems with that, but by and large, other than drivers who start out specifically as oval or off-road racers, F1 is the dream for most young drivers. I compared the skillsets of F1 and sportscars earlier and it is true that a large percentage of the F1 grid would be elite in sportscars too. But most of the time, active F1 racers don't go to Le Mans, and if they do it's midfield runners or tailenders, especially those on borrowed time in their seats, like Franck Montagny in 2007 or Sébastien Bourdais in 2009. For the most part, active F1 drivers don't need to go to Le Mans, it just gets in the way of their goals.
But there's only 20 or so seats in F1, and there are, what, 159 seats available at Le Mans? 53 cars with 3 drivers each. Now filter that down to around 125 once you take out the gentleman drivers and hobbyists in the Pro-Am cars, but it's still a larger number of opportunities. Many older ex-F1 drivers and those who never made it fill those seats, but also quite a few young prospects trying to build experience in case their F1 dream doesn't succeed - but also a lot of solid drivers who are good enough to be pros, but not good enough to make it up to F1. Gravel cycling is kind of in a similar position to sportscar racing in that respect; the very top elite riders in the disciplines that make the most money aren't entering gravel races, the only time you see active WT pros in gravel are journeymen - but you will see a lot of ex-WT pros, some young riders trying out different disciplines to find one that suits them, and a lot of people straddling the pro-am boundaries where they can probably make a better living from it than they can as a domestic pro in the Continental scene of .1 and .2 races.
The problem is that when it comes to the converts from road, you're playing with people a bit further down the pecking order, so to speak, because there's far more riders at the WT level than there are drivers at the F1 level in my comparison. And the other problem is that Le Mans has over 100 years of history so its prestige is at least recognised, even if the average man in the street has much more chance of knowing who Jacques Villeneuve is than who Tom Kristensen is. Gravel is still establishing its own character and history and so winning these events doesn't confer the same status and prestige to the casual fanbase as a win at Le Mans does on a racing driver.
The other side is, I believe that the UCI's vision of gravel is more like the Daytona 24h than the Le Mans 24h. Daytona is something of an oddity in the motorsports calendar, it's part of the Grand Am series (or whatever it's called now) but is oddly separate from it. The event has much more lax rules on repairs, lap completion, driver shifts and drivers per car than Le Mans. In fact, one year, the winning car had no fewer than 7 drivers, because they allow 4 per car (as opposed to 3 in Le Mans and the other WEC events), but also they allow substitutions for drivers who haven't participated so when the team's other car crashed out early, three of its four drivers who hadn't entered the race yet joined the car's driver lineup. It's a nice touch, that everybody got to participate, but it also does devalue the endurance when, while the car still had to last 24 hours, the drivers were only doing an average of 3 and a half hours each, as opposed to 6 for other teams in the same race, or 8 at Le Mans.
But, as a result of this and its position on the calendar (right at the start of the season), the Daytona 24h has become something of a festival atmosphere, with a large number of superstar NASCAR and Indycar drivers moonlighting in the teams as one-offs, and increasing star power, but at the expense that it doesn't have the same feeling of a 'true' endurance event and is viewed as significantly less prestigious than Le Mans where most of the biggest teams have well established 'factory' lineups and this type of moonlighting bonus star is a rarity (even Fernando Alonso in the Toyota did a whole season of racing, the last real notable one would probably be Nico Hülkenberg in the Porsche) - and a lot of the fans that come to watch it come to see the guest drivers as much, if not more than, the regular Grand Am field who will be duking it out the rest of the season in these vehicles.
Likewise I think the UCI has this idea of the Gravel World Championships as a sort of season-end (summer disciplines)/season-start (cross) multi-discipline festival where they deliver something that offers a bit for the roadie, a bit for the crosser, a bit for the MTB specialist, and they can all get together and duke it out a bit - so they don't want it to be a proper 300km endurance slugfest dominated by riders that the general public haven't heard of, that they themselves have not marketed, and that they have very little by way of drug testing info on. They would much rather it be simplified enough that they can sell it to the public via races (look guys, it's like Strade Bianche or Tro Bro Léon, but
more so!) and faces they are already familiar with. And who are those faces? Why, the people that win the races in the more established disciplines of course!
But as long as the format is not priority #1 for those riders, they aren't going to be enticed to do what you would perceive as a 'proper' gravel course in terms of the distance, because that would require more specialised training, much as back in the day things like Bordeaux-Paris required specialist training. And of course the UCI has shown from other disciplines that it is all about trying to get shorter and more explosive races to make things more easily televised, and easier to follow for the novice fan (because pretty much everybody in the audience is a novice fan to this as a TV discipline) so you get these courses that are shorter and designed to be more explosive. I don't think it's so much about these courses being 'easier', just different.