I can recall a time when the French used to have halfbacks throwing the ball in.
Indeed they did. I remember the current Racing Metro coach, Pierre Berbezier, throwing to the lineout in the 1987 RWC and he was their scrummie.
I had a look back at some of my archived games involving France and in 1958, 1961, 1964, 1968, and 1971 they used the winger to throw the ball in. They changed in 1973 to use the hooker, but in 1979 they used the winger again.
This swapping, and swapping back, during the transition was fairly common. The change from winger to hooker started in the mid 60s and by the end of the 70s most had changed to hooker permanently, but there were exceptions. Béziers, the dominant force in French rugby from the early 1970s to the mid 80s, used a scrummie to throw to the lineout; so that is probably why France was the odd man out for a while.
But the winger didn't always throw the ball into the lineout. In the old days teams used two scrummies, one for each side of the scrum and around 1890 most teams were using one of them to throw the ball in .
In 1905 the All Blacks, who used only one scrummie, toured Britain and they used a short forward to throw the ball in. They used the lineout to launch attacks and needed their half back to be there to pass the ball. In Britain the locals typically got the ball on the ground and advanced it up the field at their feet, in what was called a loose scrum. Mauling as we call it now was illegal – but I digress.
What the All Blacks did amazed them up north but they kept using the half back to throw in for a long time, but after WWII the winger started to be used more and more to do the job. They had the speed to whip out to support the backs running with the ball and if a lineout was lost they were fast enough to run back to help out there to.
I remember reading comments in the paper that this winger or that was a better choice because he was more accurate thrower; so in the days or Rafferty's Rules lineouts their throwing skill was highly prized.
Then the rugby world changed and much of it had to do with the abolition, in the late 1950s, of the tackled ball law, an archaic relic from the olden times of rugby. This was one of the most significant law changes in the history of the game and it had effects all over the park which were not expected but were generally good for the sport.
One of the side effects was that set pieces became more valuable; so the wingers became used for set piece attack more often. Therefore the short forwards came back into the frame to throw the ball into the lineout. Because the props had their jobs to do in the scrum and the hookers didn't push but hooked for the ball (because the scrum put in was straight in those days), the more rested hooker got the job.