I was riding with my brother in his new Mazda3 and after observing his style, I'll tell you why they are rated so much lower. It's more than just holding power.
Let's say you had a 5,600# trailer behind a 5-speed Ranger. You get it going from a stop and that warms the clutch up quite a bit because you expect it to get the hell going and have lot of revs and are taking a lot of time getting the clutch clamped. Then you run it up to 3500 rpm, shift and let the clutch back out. Your transmission wants to see the engine at 2100rpm and you have the engine still over 3000rpm--and you are pusing the accelerator with the rpms mismatched to boot, making it worse because the clutch can't fight the tranny back down to 2100 when you are pressing on the gas. So you heat the clutch up massively more while it tries to pull the engine down to 2100rpm and you won't let it. Every gear a person used to driving a Mazda3 hits, the clutch is suffering, badly. When you are pulling something, you really only need to let the clutch slip when you start from a stop. Then you let the engine fall to where the tranny is before letting it back out. The clutch never has to get hot--when you figure the rpms out you can pop the clutch up hard and not feel it engage. When you first take off, be merciful--use lots of clutch and let the engine's low rpm torque work. After it's engaged, accelerate. It doesn't take a whole intersection to get it going. I'm almost lugging it at first. Then it's zoom up, clutch in, pause for the needle to fall, clutch out, zoom up. If you hack at it like my brother, and add a 6,000# trailer, your clutch won't last.
Since an auto shifts instantly and has a converter to double your 0 mph torque, it's better. But you can drive a manual to last longer because the auto Ford put in the RBV is a stinker. They took the one that was easier to adapt for overdrive and a lockup converter and no the stronger one.