Mac, I'm with you on this one.
If the distance is under 5 yards and the buck shot enters as one big lump, yes, maybe it would be ok.
But if you're back to a single projectile you may as well use a large cal double rifle unless as Will says that perhaps the shottie is lighter and maybe easier/faster to use.

In the late 70's I shot a lot of good size boar pigs using a Win model 1200 18" pump and S&B 00 buckshot.
Side on chest shots at 15 yards worked real well and killed.
Frontal shots into the chest at 1 yard worked real well also and pulled 'em up fast and the big single entry hole would smoke for a short while afterward!

But, rear on shots at pigs running directly away were totally hopeless and I lost a lot of good boars that way.

I have no experience with African big cats but if I had to face a wounded one, give me a big double rifle and softpoint bullets please rather than a shotgun.