If you was planting say,a 1/2 acre or so,at a time,yeah,a potato plow or something like that would be good at making furrows and save you back.
But most people plant many different things at different times in less than 1/2 acre,so,if you had a 1/2 acre garden[like me] and you tilled it up good and than made furrows in all of it,well,it would be a waste of time,[for me anyways],just have to do it again when I tilled again and planted corn and beans.
Its at least a month between potato planting and corn planting,with other things in between and other stuff even after corn.
Plus,some things you plant in shallow furrow and some things you plant in deeper furrow.And somethings you plant in a hill of some sort.
I made three stakes out of about 1/2-3/4 steel rod[one for each end and one in center to hold line up] put handles on them for to push into ground,sharpened the ends. Wind the string around the handles on the end ones.
Got a horse tiller to go between rows to weed and to break up ground to hoe,after I till it with my 5 ft kk tractor tiller to begin with.
Make the row spacing about 1 1/2 times horses width[for most things,little wider for viney things.]