1. Shot placement is King.
2. Penetration is Queen.
3. Reliable function of the firearm is required to repeat 1 & 2 as often as necessary.
All the rest of it I have seen, heard or read almost continually since the early 1980's.
Of all the opinions I have sifted through I would add that of Walter D.M. "Karamojo" Bell who hunted elephants with a .303, .275 Rigby or 6.5X54MS in the heyday of that trade. Shot placement is everything. A 180 grain bullet precisely placed is fully adequate. A 500 grain bullet less properly placed can make life exciting.