Greetings!
Comparing the powder charges, there really isn't a "tremendous" velocity difference between the two cartridges, it being 100 / 150fps between them. Perhaps the .44 HRF more efficiently ignited a greater area of its smaller BP charge...
The biggest draw to the .44WCF is the ease to which it can be reloaded; also, the cartridge, its bullets bearing surface and lubricant being protected by virtue of its being seated in the neck of the shell, can be subjected to more rough handling than the .44HRF.
Although the 1873 is the stronger and more advanced, those that didn't shoot a lot may have been satisfied with their Henry / 1866 long guns. Perhaps Winchester was surprised that well after the 1873 had become established as a technological improvement, they continued to sell the 1866 ( "Improved Henry" ) into the 1890's.
Also, if you look at the old ammunition prices, you'll see that formerly .44HRF was noticeably cheaper than the .44WCF; but later, .44WCF became far more popular, and cheaper.
As fighting cartridges, they both look good. They're also decent "food cartridges", in that accuracy is adequate for headshots on all small game, and, at shorter ranges, could take deer humanely...
M.T.M.