I think the V3 problem was simply not enough badge creed in the space where it competed (M5, E63 AMG, etc...),
The V3 was in no man land, too expensive for someone looking for cheap thrills (the Hellcat is a lot of bang for your buck at 65K but it ain't a M5 or AMG rival, imagine an hypothetical supercharged Chevy SS for a comparison) and not enough brand recognition to play at the same level with the big boys (from a marketing/public perception standpoint not on product and road dynamics where it is even better on some regards).
Mopar has definitely a larger fan base and it is positioned at a significantly lower price, on the other side, as i said already, many looking to spend north of 100K want the proper badge which Cadillac does not have or regained from a glorious past yet so if dealers wanted to move their V3 inventory they had to price them aggressively. With the V3 the business model has been the typical "push the product to the dealers" one. In contrast, I was looking at the new Audi RS6 and you know how many were allocated to the largest Audi dealer in Seattle for 2020?? Only 4...four with a pre-approved waiting list of over 20 people for that dealer....forget about discounts. But the Germans have the brand strength to pull that off, they can "afford" to operate in this way in the uber segments and get top dollars...even if the depreciation at the end is probably even worse than a Cadillac V car in the long run.
Interestingly enough, FCA is running into the same problem with the Jeep Trackhawk I'm shopping for my wife......I got a written proposal to get one on order for 10% off MSRP, many dealers are listing just arrived 2020s for 6 grand off and sometimes more....it was priced a bit too ambitiously, there are not many potential customers for a 100K (or close to 100K) Jeep, the market is still full of new 2018s sitting on dealer lots and some let them go for well over 20K off MSRP. Many dealers actually now refuse to stock them (there is only one Trackhawk left in the entire Northwest, from the Oregon-California border all the way to Canada) because it is a slow seller...the Germans definitely own that segment of the market.