Seems to me that saying a hot, heavy loaded 45LC is equal to a 45-70 on the bottom end is like saying a hot, heavy loaded (ie, 165gr. bullet) 300Savage is like the 30-06 at the bottom end......yep, they both get similar velo, trajectories and performance, but the 300Savage is never going to be a 30-06, no matter how much it wants to.......
But a man's got to know what he wants; if that level of performance is all you want and/or need, that is OK by me, and I do that kind of analysis and decision making myself. I shoot a lot more cast bullet 357Mag loads than I do full on 45-70.