Some places in Africa (and elsewhere) require absurd energy levels for game, levels that were not commonly attainable even 140 years ago... when plenty of people had little trouble killing off the wildlife lol. The problem is that often times the people setting the reg's often are not intimately involved in the thing they are regulating, and by extension, make bad calls. Basing things off of bore size or energy (the bulk of reg's in places that try to dictate equipment) is not responsible regulation (we know there is far more to determining suitability of arms and munitions than bore size and KE); likewise, simply using the regulations to decide what is the "ideal" weapon for the animal you are hunting is a irresponsible hunting. You owe it to the animals to research them (and similar species), and figure out a solution that will work for you (and keep you out of trouble with the law...ugh).
I primarily hunt with BP guns, particularly muzzleloading guns, and there's a lot of stuff I can't use in some places in the world... not because it doesn't/hasn't worked, but because some politicians/bureaucrats have decreed that magically, the effective weapons of yesteryear don't work... apparently, the animals are all wearing body armor these days lol.
Now personally- Tiger, Lion, Buff, Ele, Hippo (and non dangerous game over 1900lbs); I'm not going out with less than a .50 (maybe .40 on large non-DG (ie: eland)), but then again, I hunt with BP and heavy lead (African Buff are typically hunted a little differently than other large bovine, the places you can get close enough to them often puts you in close proximity to them w/ limited visibility, ditto with Lion and Tiger, if it were like the American Plains, I'd say even BP .40-70 would work lol). There seems to be a trend amongst sport-hunters (and companies/politicians/writers) to "magnumize" everything, and provide the impression that nothing but the biggest, baddest gun will make even a dent in a little Duiker or average American WT deer lol. The reality is, living things don't live too long with a hole running all, or most of the way through their chest, so long as you are 99+% confident your weapon will kill the animal efficiently at the range you are hunting at, I don't see what the issue is (just be ready to run if it comes after your lol, then again, having a bigger gun won't necessarily solve that issue)? Just my opinion, I suppose