I think in terms of pure physical and mental, attrition, not really skill, it goes
1. 70 hour rule and forced Saturday helpers which is just downright unhealthy number of hours.
2. Any number of standard operation inside jobs that adds up to greater than 8-9 shifts in 1 week. Physical burnout.
3. delivery drivers under 60 hours. which is a 50/50 split of physical and mental burnout, but both to a slightly lesser degree
4. 22.3 combos who can either skate with 8 or have clerical duty. mechanics also might go here
5. Load/Unload and preload. Decent preloaders trade a tiny piece of labor for extra mental exhaustion. but you get to stop work around 4 to 6 hours.
6. sort and irregs
7. car wash, yard shifters and feeders
8. the remaining gravy jobs.