If you seriously think you may have to fight off a cougar then you should seriously think about carrying a gun - they're much more effective. If you can't/won't/don't carry a gun then there's nothing wrong with just a knife. How a person carrys their knife is no big deal, I'm all about whatever works best and that usually varies by individual situation.
I don't think its a matter of thinking there's a likelihood of going to battle with a lion as much as it's a recognition that something as simple as moving the carry location of your knife could improve your chances of survival on the off chance a lion encounter did occur.
It's recognizing and implementing a simple, no-cost, low effort risk mitigation measure for a low probability, but high impact risk. For me this is a good balance; I don't think the probability of such an encounter really warrants a specialized defence tool.
That said, the specific situation can change things; I had started planning a trip to one of our national parks earlier this year and the park had issued a warning that a mountain lion was frequenting high use areas and recommended all visitors carry bear spray due to the increased chance of an encounter.
Wouldn't a tall backpack and hiking staff be better for the ( incredibly unlikely, really really close to non-exixtant) cougar/ big cat attack scenario?
I think a tall backpack would definitely help; I'd think it would protect you from most of the initial injuries that would come from the type of ambush from behind/above that seems common. As for the staff, I think it might be helpful in the situation where a lion was being more overt in its actions or where you had to try and break the attack of a lion on a friend or family member, but might not do much good if a lion was on you.
From what I've read so far, it appears that the situations where knives proved the most helpful where those where the lion was on the victim and they used the knife to stop the lion's attack themselves.
One thing I've noticed is that a lot of people don't hike with actual hiking sticks/staves anymore. Instead they use lightweight collapsible hiking poles modeled after ski poles. While great for hiking stability, they don't make for very good weapons.
I love my simple, wooden hiking staff. I've been considering switching to a more modern solution primarily for the compactness and packability, but I just can't get over the benefits of a simple wooden staff ... but that's getting way off topic ... hijacking the hijack