I'm not disputing it, but just pointing out that there isn't much written about taking deer with TB powder, and what is the most you can pack into a 45-70 case using a 405 grain cast bullet? You are limited to a low end of velocity, and you won't get 1500 fps with a 405 grain bullet using TB, where even using black powder you can achieve a higher velocity than with TB.
Why isn't it not used that much for taking deer?....I can only speculate, and that is because there are better choices, and bumping it up to 1500 fps with another powder that recoils like black powder loads it just makes more sense.
That said, I load with TB powder, but I also use IMR 4198 and RL7.
I hunt with the later and plink with the TB, and my loads run from 1200 to just under 1500 fps. I don't like a lot of recoil.
I have shot two fairly large hogs, not with the 45-70 but another 30 caliber rifle using TB and never found either hog. Probably just me, but I don't lose any using my standard loads.