This payload sticker was posted by the owner who is on this forum. It is for a Trialmaster with Safari windows, but not with a winch [slight edit]. The payload is 1,376 pounds (624 kg).
It is worth remembering that the specs in the Ineos brochure are for
maximum possible payload (and maximum possible towing), which is how all manufacturers present payload and towing specs for their vehicles. For the petrol Grenadier, max payload is 1,916 pounds (871 kg), which is right around what they promised all those years ago (the stated goal during vehicle development was 2,000 pounds).
However, almost no one ever buys a vehicle with the max specs, because pretty much every option a buyer ticks adds weight to the vehicle, thereby decreasing its payload.
A payload of 1,376 pounds for a midsize 4x4 is considered very good in the North American market (we don't have the 70-series Landcruiser here, which is a payload beast).
A Jeep Wrangler Rubicon - similarly equipped to the Trialmaster mentioned above - will have a payload of around 850-880 pounds (steel bumpers, lockers, no winch).
A lot of similarly equipped midsize pickup trucks (e.g. Tacoma, Gladiator) will have payloads around 1,000-1,200 pounds; I just looked at a Gladiator Rubicon with a payload of 1,083 pounds, and my Tacoma is 1,100 pounds. The Ford Ranger does quite a bit better: 1,200- 1,800 pounds - depending on options.
A well-equipped Power Wagon - which is clearly in a different class of vehicle - with solid axles front and rear, lockers front and rear, steel bumpers, a winch, heated seats, and a spray-in bedliner - has a payload of 1,510 pounds. The frame and full-float axles on the Power Wagon are heavy duty, and are the exact same frame and axles that are spec'd to carry a payload of over 4,000 pounds on other Ram 2500s. The limiting factor with the Power Wagon is its suspension: the springs are soft in order to achieve maximum articulation off-road. A very easy spring swap can get you a functional payload of 2,000 pounds - if that is something an owner wanted to do.
Conclusion: the Trialmaster version results in a drop in payload from 1,916 pounds (base petrol Grenadier), to 1,376 pounds. That's a drop of 540 pounds (without a winch). I would guess that you lose another 50-75 pounds with a winch. But nevertheless, a payload of 1,300 - 1,400 pounds for a "triple-locked" midsize 4x4 (here in North America) is quite good.