The .30-30, once they figured it out, proved to be more effective than a .45-70. What's changed since then is a few hundred fps have been added to the .45-70, but not enough to make it faster than a .30-30. Does the .45-70 with heavy bullets penetrate big bears better? Yes, but there's 458's for that and the 458's wound more decisively. For just about anything else, .30-30 is still better, and it's got to be one of the wimpiest smallbore rifle cartridges out there.
The .45-70 could be fun, it can certain take game, and it's traditional, but there are cartridges that do everything better. Now if it was necked-down to .33 Winchester, it would make a good rimmed deer cartridge for lever actions and single-shots, but not quite as good as the .348 Winchester. The .348 is useful all-around and with a bullet suitable to the task, a better choice than .45-70 for anything except maybe big bear defense for which the 45-70 still leaves a lot to be desired. Still, I think a lot of 45-70's sell for reasons other than big "bears." If it's for nostalgia, it's easy to understand. The 45-70 certainly has a place in history but as a "modern" cartridge, no, it's lame.