Your unicorn exists.
It is called the Toyota Land Cruiser. It continually, as it always has, sets the bar for SUVs. It sets it in performance, reliability, durability, comfort, safety, and, oh yea, price.
While it's difficult to find the safety ratings for it by the IIHS because they haven't tested it since the new model came out in '15. The 2015 Land Cruiser received near perfect marks by the European IIHS equivalent, ANCAP. They have a similar test to the small offset frontal collision test that they call simply the "Pole Test". The Land Cruiser was one of the only vehicles tested by ANCAP to receive perfect marks in that category. It is a beast of a truck. No diesel option, but it uses a 380 hp, 400 tq 5.7 Liter Toyota V8, built in conjunction with Yamaha, and it is no slouch. It only comes in Full Time REAL 4WD, and it is hard to beat as an off-road capable monster. The only caveat, as I alluded to earlier, is the price. It starts, and also pretty much ends, at around $85,000. That said, there are no packages, no extra configuration options, no optional accessories. It is Toyota throwing every bit of tech and performance that they have into an SUV and slapping a window sticker on it. It only comes with everything. Outside of this, yes, I do belive you may be searching for a unicorn. The GMC Yukon Denali gets close, but I don't know that I would give it a go off road. It definitely feels like more of an on-road SUV in my opinion. The Sequoia, and possibly the Armada, though it badly needs an update, would be the other possibilities that I could see honestly. The old Ford Excursion was always a nice choice, and you had the diesel option, but it went the way of the dinosaur a while back.
I feel that it's worth noting that I currently own, and regularly drive and abuse a 2001 Toyota Sequoia Limited 4WD. It is fully loaded, even down to having the very rare Gold Package. It just rolled to 270,000 miles, and she still starts up every time and she enjoys the beating. I'm not particularly nice to her, including taking her off road, albeit relatively infrequently, but she seems to enjoy it and just keeps on going without a fuss.