Had a think about it as I've read this thread a few times, and then the penny dropped.... I've been doing some support work for a 1st year/4th year Economics unit, and this clicked.
Theoretically prices (demand side) are determined by:
-Price of the product
-Price of substitutes
-Income
At a supply side, they're a bit messier, as it's more to do with the cost of production, but in the used market it's going to be something related to the cost to change and perceived value, as well as the need to sell. Also, the used market has a relatively finite number of vehicles in it as there are only x number of (say) 2017MY Jeeps in this colour and those variables can't suddenly change, leads the market to being relatively inelastic (so a change in demand only has a small change in the quantity, but a bigger change in the price) As more and more people need to sell, the less inelastic that supply comes to a point.
Now their are points in both cases that are going to be quite important - stimulus cheques dry up, and incomes fall. At first, the stimulus cheques will have bumped up the spend on "toys" as people can afford to spend a bit more on things that they may not otherwise have bought. BUT once that dries up, there is then a need to realise/liquidise assets to pay more crucial bills and that will push prices down.
So, all up? I think that the novelty of the Bronco would have had a short term blip in the first instance where it would push the price of the substitute down (so that FCA can maintain volume numbers at the cost of turnover value - you need the economy of scale to be efficient in automotive manufacturing more than you need turnover to put a value on the books) BUT that was in the world pre-January 2020. Now? I think that the Bronco is going to be really pushing the price of a new Jeep downwards - but in turn, that will pull the price of the Bronco downwards as well because otherwise they will lose too many sales to the cheaper Jeep... and this is where Land Rover may have been shrewd with the Defender, as it will probably stay out of that market, sitting in a (potentially) less price sensitive market.
Finally, People are driven by conspicuous consumption; that's one of the reasons for why the Toyota Prius killed the Honda Civic hybrid - the Toyota was noticeably different, whereas the Civic looked like the rest of the range. A Jeep Wrangler to 99% of the population looks the same from the JK to the JL; therefore, how do you show you got a new one? In contrast, the Bronco is brand new, and likewise the Defender. So with that, you have the "look at me I've just spent $50k on a new 4x4" and the "look at me I've just spent $70k on a new 4x4" markets with the Bronco and Defender respectively. The Jeep? Well, no one would ever know you've just bought a new one... so how do you use that to show you have a job/money?