"What interested me about the stats I found, though, was that some breeds were clearly more likely to cause fatal injury than one would expect given their relative popularity. This is probably due to an extent to the relative size and power of the dogs, but it's also interesting that some large breeds don't figure in these stats."
The issue is that the stats are all flawed...
There's no real way of knowing how many pit bulls there are in the us for instance, for the same reason that they can only estimate staffies here...
The registered ones are not most of the population, there are thousands (possibly millions in the US) of not kc registered dogs, plus crosses and anything that looks vaguely similar and they'll all count as pit bulls as far as reports of attacks.
Plus, you're looking at fatal attacks, they're rare, they're hard to actually pull anything meaningful from as far as breed goes.
There are studies that show common factors in fatal attacks, they disregarded breed as a factor after looking at them because it wasn't statistically significant - things like a history of abuse and neglect, the victim not living with the dog and the dog's owner not being present came top.
You've also got to factor in the owner... what sort of person owns wolf hybrids? It isn't someone looking for a family pet, it's not even a domesticated animal, nevermind a pet.
Sadly, breeds with a reputation for aggression do attract owners who are more likely to create a problematic dog alongside the more normal owners.
With just bites, the reason there aren't many stats on breed is that they're too hard to collect, in most cases you'd be relying on victim or witness identification, people are not great at identifying dog breeds, again crosses of lots of breeds are likely to be described as a pit bull or staffy...even if they're actually a lab cross.
Anecdotally I know a Great Dane owner who has been asked more than once if he's a Dalmatian, I've been asked if my Rottie is a black lab and a mastiff - he is a completely normal looking Black and Tan Rottie.
And again I'm going to point out that soft mouthed does not refer to bite strength or willingness to bite - it specifically refers to how they carry things, it's irrelevant in a pet dog, they won't be carrying people.