So, what you guys seem to be saying is that if you don't load your own ammo then the 45/70 doesn't hit hard enough?
Well there are some 'warm' factory offerings out there, but few. 'Hard enough' is a relative term.

People have killed big bears with 44 mags and 45 colts, so realistically even factory 45-70's are hotter than that.
But a quality shotgun slug is a pretty damn devistating thing to get hit upside the head with at close range too. So, it's kind of a bit of a close race in a defensive situation.
It has often been said that all else being equal a rifle is a better choice. However - the REAL answer will depend on your personal situation. For example - if you've shot shotguns all your life, hunted with them etc, and never used a lever gun you would probably be WAY better off with the shottie. There was an account posted recently where a guy borrowed a marlin guide gun for bears and hadnt' used one before, and when it came to the crunch he forgot a saftey, couldnt' figure it out in time and the bear mauled him. That guy would have been better off with something he knew.
Likewise, i spoke to an alaskan guide who prefered his 44 mag pistol to a shotgun for a light 'everyday' carry, whereas his buddy always carried a shotgun. When i asked him why he said he'd noticed in practice he had a bad habit of short-stroking the shotgun, whereas he was a deadly shot with his pistol and practiced enough to use it in his sleep. He knew the shotgun was 'better', but it wasn't 'better for him'.
I'll tell you this much - having talked to a lot of guides and other 'experts', and reading the accounts of who is and is not successful defending themselves with a gun, the shooter is more important than the gun. Which ever gun you can shoot better, prefer to carry, PRACTICE with religiously, THAT is the gun that is probably the best choice for you.
I've shot shotties all my life and can shoot them pretty good. I've never owned a lever gun, and have shot less than maybe a dozen rounds thru any. So if i were going into the woods today i'd rather have my shotgun vs ANY lever gun. Because a shotgun used well will beat a 45-70 used badly any day of the week.