I'm not trying to make a moral argument, I'm just saying that those that fall prey to hyenas suffer much more than if they had fallen prey to a number of other predators that tend to kill swiftly before eating (feline predators and snakes for example kill quickly; many birds also tend to kill on the first strike).

Hyenas don't bother killing, they just eat, and tend to start from non-vital organs, of all places, which is quite different from what most predators would do.

I'm no wildlife biologist but it seems that hyenas are not big enough to take down some of their prey by the neck (without high risk of injury to themselves, where a broken leg probably means certain death), so the evolutionary adaptation is to go for the soft underbelly. Undoubtedly the prey animals do feel pain and suffer.