As I said in my original reply I suspect the RS6 C7 will continue to devalue at it's current rate.
As far as the statistics are concerned, I can't help but feel some people are trying too hard to poo poo them without actually taking notice of what they tell us.
Clearly, if you live in an enclave of 4 houses and all 4 own an RS6 C7 you're going to think they're as common as chips but the fact remains there are only 2800 in the UK. The point of comparing that to other marques was to suggest the obvious... Statistically therefore you stand as much chance of seeing a Lambourghini (of any model) on the road as you do another C7. Value of vehicle is totally irrelevant for this. The fact of introducing more 'common' marques was to illustrate you're twice as likely to see a Rolls Royce and three times as likely to see a Bentley etc.
Of course there's other factors to take into account such as an RS6 C7 is far more likely to be a daily driver than a Lambourghini and so in reality of course you're more likely to see a C7 but you cannot argue with the fact an RS6 C7 is relatively rare which someone was suggesting they're not.
If you still want to make out the illustration makes no sense then I can't help any further.
Oh, and as the market increases for them (due to the price becoming more affordable) they will be in higher demand which in turn will prop the price up. There can't be a market awash with them as there's only 2800 to go around
Best.