APPLES vs. ORANGES....
I've got both, sorta.....
I've got a Marlin 1895GG, AND, I've got a Marlin 338MX, and fwiw a MkX Mauser in .338/06....
For the obvious use, yes, at ranges under 100yds with either a heavy handload, or one of the custom factory loads you can get some near-.458winmag performance from the .45/70. I've shot some 400gr loads at near 2,000fps (remember 18.5"bbl) and power and penetration are awesome. Recoil has to be expected!
However, with the .338Fed (and it's rimmed equivalent the .338MarlinExpress), with the available bullets, the trajectory at 300yds is much, much flatter and recoil is much tamer (eq. to the .30/06).
Kinetic energy (ft/lbs) favors the .338Fed (.338ME), but momentum (lb/ft) favors the .45/70. It is well documented that the momentum calculation better describes the performance of large bullets on large game. For black bear and deer size game, the ft/lbs is better.
So, to MY conclusion:
Different tools for different jobs.
To walk into an alder thicket to take/dispatch a LARGE bear- give me my 1895GG; it wears both the original rear sight, and a Williams Guide-reciever sight as well as a Williams Fire sight front sight. I also have a Leupold base, rings and a Leupold VX-III 1.5-5x scope that can be screwed on the reciever as desired. I've got a heavy load... 400gr hard cast, heat treated FN over full case of IMR3031. And, a "working" load of 300gr FNGC (weighs 320gr as cast) over 30.0gr of #2400 for an inexpensive "do all" load, from plinking to deer hunting. (chrono's 1,650fps and shoot sub-2moa at 100yds)
To walk the ridges and dark timber of the western rocky mt. or the oak-pine bottoms of the S.E.USA, with the possibility of a 200-300yd shot on a deer, pig, elk, black bear along a powerline or gasline ROW, and at same time to handle a bear that tries to get into the tent with me at 3am, -I'll take the .338ME, or if YOU prefer, an AR platform in .338FED. Give the .338FED a Nosler 210gr Partition and you're "adequately" equiped for anything in N.America. The whole reason for it's existence (and Marlin .338MX).
Efficient packaging of a proven commodity. My MarlinMX weighs 8.6lbs with Leupold VariX-II scope and 5rds of ammo. The MkX weighs 10.5lbs and is 5" longer...
And yes, if in Alaska, my first round in the barrel will have a Nosler 210gr Partition over 46.0gr of Acc#2520. Gets 2,450fps mv. Hits 1" higher and to the left of the 200gr FTX at 100yds.