They are treated far better than lorry drivers
The purpose of DHL Air, or EAT, is to provide transport of packages. In other words, while airlines have a business plan founded on transporting passengers, DHL operate aircraft because it is the only way to get boxes from A to B fast enough. Trust you me, if there was a cheaper way to get a box from A to B as quick as flying it, it would be done.
Now the longest sector DHL Air pilots fly is around 3 hours. EAT do operate longer sectors with the Busses and the PF, but they are fully catered. If someone can not go for 3 hours without stuffing themselves, well, maybe a diet is in order?