"So if this kind of vehicle is becoming the norm, then does a manufacturer stand to gain more benefit from advertising the car as something that can rip along a few roads, over a couple of days, faster than its rival, or would it look better if it dominated it over a (still quick) event that celebrated more of a reliability victory?"

Really someone is still thinking you sell a car for a reason different than advertising?. How many cars are sold because of winning the Dakar? Not that much. How many because is the car of mr.x instagram influencer? Way more. In the end, there's no difference between sprint or endurance, selling-wise. the point is to be on the news, possibly winning. and the general customer doesn't care how the rally is done. it's just a rally winning car.
Then the point goes to generating a big enough audience to be relevant for the markets. How you do? Marketing! Media as prime option, then events. TV and internet. Nothing long is really working nowadays there -not liking it either, but it is how it is-. you have 2 ways then: working on the general or became a very strong niche. they're working on the big numbers because the manufacturers want it. let's face reality: how was rally heritage useful for lancia or fiat/fca in the last decade? zero. not even to save world most known and winning brand. one thing is what we like, or we would like. Another thing is nowadays world. Rally needs lots of money. Rally needs investors. They follow the market. at the moment market demands very fast and very catchy short content. not time for hardcore fans niche. not time to go there. best example '17 cars: not in the spirit of pure rally: too focused on sprint and speed, too aesthetic. they worked for media and non-fans. still not enough to move real things, but starting.
Events: short spectacular things, concert/live events philosophy. Not having people in the woods, having them in a square (stadium?), with food, drink, gadgets and -again- media. You can't sell 100k people in 50 km street. You sell 100k people in a square, let's say end of a power stage maybe? Then brands will give you cash to have their name there. again: not liking it, but it is what it is.
Becoming a strong niche would be great, but you need big money to start, and again that's not the time.