I felt like the multiple blacksmiths was because they wanted to give you that function in your castle early on, but couldn't have the player grinding and massively overlevelling their weapons. Also, they must not yet have thought of the hammer system haha.
I think the hammer system actually works fairly better, it's a lot cleaner, and as mentioned, you have more room for other interesting characters, as opposed to basically five guys fulfilling one function. Not to say that the blacksmiths weren't interesting in their own right, they were, but it's a little like using five stars of destiny for the squirrels in SII or the dogs in SIII. Space could be used for much more interesting characters. They also didn't have as much personality as say the beavers from SV, but I suppose that's a function of the games coming out in different generations.
That being said, blacksmiths definitely need to be recruited earlier on in the game haha that's for sure.