Counter-intuitive tyre wear...
 

Rear tyres after about 300km (186 miles) from new. (Pirelli P1's with with a 1.5 OS Giken LSD fitted)
Of that total, aprox 110km (66miles), over two seperate days, on a dirt rally circuit is what did the damage.
The circuit is run clockwise.... the inside rear is the most worn, the outside rear, much less so.
Its interesting and a bit counter-intuitive, as its seemingly the outside tyre that is doing all the hard work.
But, the inside rear is actually being dragged sideways, with much less weight on it, so is actually only using 30% of the tread face of the tyre...spinning across deep embedded rocks.
The outside wheel is using near %100 of its tread face, and is not dragging so much as sort of "digging" as it slides.
The circuit starts with a nice slippery gravel surface... which is quickly cut through after a couple of hours, leaving embedded rock is utterly brutal on road tyres (rally tyres being banned because they destroy the circuit base)

might be time for some adjustable lower control arms. i know my car desperately needs them. both my rear tires look like your first example...

If such wear pattern is on tarmac with mostly grip driving, i'd rather think that rears are overpumped (not that uncommon, if eg. one has fitted very wide tires of larger volume but pumps same pressures as prescribed by carmaker for stock sized tires). If control arms were meant for more camber, need of such would be indicated by extra wear of outsides of tires, not mid.

I wish there were a streetable and street legal rally type tire available in reasonable sizes, but that doesn't seem to exist.

We end up using winter tires over here for rallycross when we can't use real gravels. The tread blocks are pretty good, but they've got mushy sidewalls and soft rubber. Some of them are still pretty quick...some of them aren't very good. I've only used them on very soft and compliant dirt and I don't think they'd last long on a very gravelly abrasive surface like yours.

- Andrew

AFAIK real rally tires won't last that long too. Recalling conversation in shop about them .. they mostly are for one race. Obviously, they still can be used, but thread blocks will have worn/rounded off edges and one cannot expect competitive top grip from them anymore. No own experience on how that compares to street legal winter tires wear on gravel, but imho low loger term wear is not something to be expected from rally tires as it never was among priorities of developing it, just as with race slicks for grip driving. Top grip for stage, reinforcement to get by even punctured and throughout those jumps .. but long lasting? Doubtful.

Andrew: but shouldn't some all-seasons fit better rally use? Most of them also have winter-tires like extra thread sipes/more threadblocks, but probably not as soft rubber compound, thus maybe will last better in heat?

Yeah, it's a real frustration, the gap between a proper rally spec tyre and a usable road tyre, especially in timed rallycross type events.

I'm a little bit jealous of your winter tyres...they simply don't exist down here.

Luckily I'm not chasing times (its pointless against 4wd cars, and on a track that goes from slippery to mega grippy) so its just for for fun going stupid quickly sideways.

So after this last effort Ive decided I'm just going to get some cheap/rubbish Chinese road tyres on a spare set of rims for the rally circuit days.

Its also more the construction of this track too as it wears through the day....most of our gravel roads are nowhere near as tough on the car (and of course you can be %100 stupid on a track too :) )

Although the benefit with real rally tyres is that there are many different types and constructions. So there can be very soft gravel tyres that might only last for perhaps one rally stage, there are others that can last for a (relatively) very long time/distance. If you think of the difference between a short smooth cool European gravel stage or an extremely long rough hot East African Safari stage.
I guess the other thing is that for most of us a slightly worn rally tyre is still better than road tyres at their best in these conditions. :)