Every 19.5 setup I’ve looked at is around 4,500 lbs for the wheels and tires depends on the size. The commonly used 245/70R19.5 is usually around 4500lbs.
Yes the sticker is based on OE tire size and load rating, but it’s a good starting point. Plan on being able to add 1500-2000lbs to that number with good loading of the rear axle and 19.5’s.
Under no circumstances would I consider the OEM setup “not great”. A OEM 7K SRW rear axle is pretty impressive and why I was able to sell my 19.5 setup. Maybe a DRW is what you need to be able to call it great.