Lone Star, I've had several originals and reproductions over the years.
The reproductions handle 44-40 just fine. That need not be a concern.
I know it is a matter of individual hand geometry, but like you, I find that the Remington just doesn't work for me. The hammer is difficult to manipulate quickly and fluidly and the grip isn't quite right. And for me it doesn't balance nearly as well as a comparable Colt. I'm sure that isn't the case for everybody, but it is true for me.
Regarding your last question: The 1858 Remington was very popular and it had advantages over the Colts of the period. Unfortunately Remington came late to the cartridge party so they threw away those advantages as well as their satisfied customer base.
Colt had already secured the US military contract. S&W was already established and had a revolver than offered some serious advantages in loading and reloading over Colt.
When Remington finally made it to the market place, they were not only late but they offered no advantage over any of the established players. Secondly, they came with a house cartridge the .44 Remington which was inferior to both the .45 Colt and the .45 Schofield, but more importantly, the cartridge was not established commercially. It couldn't be found in any trading post or general store or hardware. This was a serious detriment to Remington sales on the frontier where ammo sources were likely to be few and far between. Consequently the Remington 1875 in .44 Remington caliber was not popular.
Remington got the message and decided to market their revolver in the extremely popular .44-40 Winchester round introduce concurrently with the Winchester model 1873 lever action. Supposedly, Remington decided money could be saved if they used the supply of .44 Remington barrels on hand. The barrel was sufficiently oversize to result in poor accuracy. Consequently Remington earned themselves a bad reputation, and though they corrected this mistake, they never overcame the damage done. Nevertheless, let it be said that the notorious Frank James was a big fan of the Remington.
Remington made yet another marketing mistake. They offered the 1875 in only one barrel length (long) while Colt offered several lengths and would give the customer about anything desired in a special order.
So it is easy to see why the Remington 1875 didn't do as well as it could have. Remington came late to the party. When they arrived they brought the wrong package. They then compounded that mistake by cutting the wrong corners thus earning a spotty reputation, and they didn't get around to offering a shorter barrel until the 1890's when the single action was being replaced by the double action revolver. And that is not to mention the ergonomics previously noted.
Now I do not know for a fact that Remington tried to use up their .44 Remington barrels on .44-40 revolvers. It is just what I have read. But even leaving that our of the equation, it is easy enough to see why Remington didn't do better in the handgun market of the day.
