You need to go back further still if you want to know what they did when they were building furniture entirely by hand.
Mortises were cut by chisel and mallet. It's not a very long process for someone who is doing it daily, maybe 2-3 minutes per mortise. If you had 30 of them to cut, then it took you maybe 2 hours. Labor was not priced at $100/hr then...
Aides slow you down when you can cut to a line and chop to a line.
WRT Arts and Crafts furniture, I've yet to see anything which really strikes me as being completely hand made. I think it was more along the lines of what we see coming from Denmark today, mostly machine made but with hand detailing. Likely it was a great majority machine made with some hand work. They had competition and so likely they were not doing everything by hand. I've also not seen any errors in the furniture like I do when I'm looking at really handmade furniture.
WRT truly handmade furniture, the furniture was planned to be efficient in its build. As someone who transitioned from making by machine to making nearly entirely by hand (I use some machines again) it changes how you approach certain aspects of the craft to eliminate real time sinks all the way down to stock selection.
When your working by hand you begin to greatly appreciate how much easier it is to work with a nicely chosen piece of wood, vs picking something that fits the dimension and going with it. When I look at stock I'm looking to see very little grain run out, very little knots and/or other things that are going to slow me down I'm also avoiding flat sawn lumber if at all possible.