A small sedan can hold 5 adults in a pinch, but if you always drove your average sedan with 1,000lbs inside, and stopped every house, it would wear out extremely quickly and would drive/perform awful. Moreover, most small cars aren't actually rated to hold the weight of 5 adults, despite having 5 seats.

Not every Sedan: https://www.consumerreports.org/cro/news/2013/09/the-heavy-r...

"The Ford Fusion, Honda Accord, and Mazda6 midsized sedans, for example, all have a combined load capacity of 850 lbs. for passengers and cargo."

I just picked up 900 lbs of tile and the place would refuse to put anymore in my Subaru Forester. It's a pretty substantial load with big safety ramifications if not stored well.

I don't think your expectations are correct.

Most sedans made today, the average max carry weight of a sedan is 900lb. And even at 900lb you fuel economy and performance is far less than "just fine."

Also cargo weight distribution is far different than people, with the lion share of packages being placed in the rear have of the vehicle and not evenly distributed amongst the front and rear axle.

1000lb of cargo is a lot to ask from any sedan and expect it to do it 8 hours a day, 6 days a week for 20+ years, isn't something I think you would find possible.